4WFBS120, 4WFBS350 & 4WFBS1K 4-Wire Full Bridge Terminal Input Modules

Transcription

1 4WFBS120, 4WFBS350 & 4WFBS1K 4-Wire Full Bride Terminal Input Modules User Manual Issued Copyriht Campbell Scientific Inc. Printed under licence by Campbell Scientific td. CS 887

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3 uarantee This equipment is uaranteed aainst defects in materials and workmanship. This uarantee applies for twelve months from date of delivery. We will repair or replace products which prove to be defective durin the uarantee period provided they are returned to us prepaid. The uarantee will not apply to: Equipment which has been modified or altered in any way without the written permission of Campbell Scientific Batteries Any product which has been subjected to misuse, nelect, acts of od or damae in transit. Campbell Scientific will return uaranteed equipment by surface carrier prepaid. Campbell Scientific will not reimburse the claimant for costs incurred in removin and/or reinstallin equipment. This uarantee and the Company s obliation thereunder is in lieu of all other uarantees, expressed or implied, includin those of suitability and fitness for a particular purpose. Campbell Scientific is not liable for consequential damae. Please inform us before returnin equipment and obtain a epair eference Number whether the repair is under uarantee or not. Please state the faults as clearly as possible, and if the product is out of the uarantee period it should be accompanied by a purchase order. Quotations for repairs can be iven on request. It is the policy of Campbell Scientific to protect the health of its employees and provide a safe workin environment, in support of this policy a Declaration of Hazardous Material and Decontamination form will be issued for completion. When returnin equipment, the epair eference Number must be clearly marked on the outside of the packae. Complete the Declaration of Hazardous Material and Decontamination form and ensure a completed copy is returned with your oods. Please note your epair may not be processed if you do not include a copy of this form and Campbell Scientific td reserves the riht to return oods at the customers expense. Note that oods sent air freiht are subject to Customs clearance fees which Campbell Scientific will chare to customers. In many cases, these chares are reater than the cost of the repair. Campbell Scientific td, Campbell Park, 80 Hathern oad, Shepshed, ouhborouh, E12 9X, UK Tel: +44 (0) Fax: +44 (0) support@campbellsci.co.uk

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5 PEASE EAD FIST About this manual Please note that this manual was oriinally produced by Campbell Scientific Inc. primarily for the North American market. Some spellins, weihts and measures may reflect this oriin. Some useful conversion factors: Area: 1 in 2 (square inch) = 645 mm 2 enth: 1 in. (inch) = 25.4 mm 1 ft (foot) = mm 1 yard = m 1 mile = km Mass: Pressure: Volume: 1 oz. (ounce) = lb (pound weiht) = k 1 psi (lb/in 2 ) = mb 1 UK pint = ml 1 UK allon = litres 1 US allon = litres In addition, while most of the information in the manual is correct for all countries, certain information is specific to the North American market and so may not be applicable to European users. Differences include the U.S standard external power supply details where some information (for example the AC transformer input voltae) will not be applicable for British/European use. Please note, however, that when a power supply adapter is ordered it will be suitable for use in your country. eference to some radio transmitters, diital cell phones and aerials may also not be applicable accordin to your locality. Some brackets, shields and enclosure options, includin wirin, are not sold as standard items in the European market; in some cases alternatives are offered. Details of the alternatives will be covered in separate manuals. Part numbers prefixed with a # symbol are special order parts for use with non-eu variants or for special installations. Please quote the full part number with the # when orderin. ecyclin information At the end of this product s life it should not be put in commercial or domestic refuse but sent for recyclin. Any batteries contained within the product or used durin the products life should be removed from the product and also be sent to an appropriate recyclin facility. Campbell Scientific td can advise on the recyclin of the equipment and in some cases arrane collection and the correct disposal of it, althouh chares may apply for some items or territories. For further advice or support, please contact Campbell Scientific td, or your local aent. Campbell Scientific td, Campbell Park, 80 Hathern oad, Shepshed, ouhborouh, E12 9X, UK Tel: +44 (0) Fax: +44 (0) support@campbellsci.co.uk

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7 Contents PDF viewers: These pae numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Function Specifications Measurement Concepts Quarter Bride Strain Quarter Bride Strain with 3 Wire Strain Element Quarter Bride Strain with 3 Wire Element Wirin Quarter Bride Strain with 3 Wire Element Wirin usin a multiplexer Quarter Bride Strain with 3 Wire Element Calculations Quarter Bride Strain with 3 Wire Proram Examples CBasic Prorammin Edlo Quarter Bride Strain with 2 Wire Element Quarter Bride Strain with 2 Wire Element Wirin Two Wire ¼ Bride use with Multiplexers and Equations Quarter Bride Strain with Dummy aue Quarter Bride Strain with Dummy aue Wirin Setup Quarter Bride Strain with Dummy aue Calculations Quarter Bride Strain with Dummy aue Example Prorams Quarter Bride Strain ead esistance Compensation Mathematical ead Compensation for 3-Wire, ¼ Bride Strain Mathematical ead Compensation Circuit and Equations Mathematical ead Compensation Prorams Shunt Calibration ead Compensation for 3-Wire, ¼ Bride Strain Three Wire aue Circuit with Shunt Math for Shunt Calibration of 3-Wire, ¼ Bride Strain Circuits Example Prorams for Shunt Calibration of 3-Wire, ¼ Bride Strain Circuits ead Compensation usin Quarter Bride Strain with 2 Wire Element Calculation of Strain for ¼ Bride Circuits i

8 Fiures 1-1. Terminal Input Module with C Schematic Strain definition Three wire quarter bride strain circuit wire ¼ bride strain wirin wire ¼ bride strain with multiplexer wirin Two wire quarter bride strain circuit Wirin for 2-wire aues Quarter bride strain circuit with dummy aue ¼ bride strain with remote dummy aue ¼ bride strain with dummy aue at dataloer Three wire ¼ bride strain circuit Shuntin remotely across active aue Circuit for shuntin across dummy resistor Wirin for shunt across dummy resistor Two wire quarter bride strain circuit Strain aue in full bride Table 4-1. Input ocations Used in C10(X), 21X, and C7 Examples ii

9 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) 1. Function The 4WFBS120, 4WFBS350, and 4WFBS1K Terminal Input Modules (TIM) complete a full Wheatstone bride for a sinle strain aue or other sensor that acts as a sinle variable resistor. The difference between the three models is in the resistor that matches the nominal resistance of a 120 ohm, 350 ohm, or 1000 ohm quarter bride strain aue. It can also be used to complete the back half of a Wheatstone bride for use in a ¼ bride strain circuit (1 active element) usin a dummy aue, or in a ½ bride strain circuit (2 active elements). 2. Specifications Fiure 1-1. Terminal Input Module with C1000 2:1 esistive Divider esistors: 1 kω/1 kω atio 25 C: ±0.01% atio temperature coefficient: 0.5 ppm/ C (-55 C to 85 C) Power ratin per element: C Completion esistor: 120, 350, or 1000 Ω 25 C: ±0.01% Temperature coefficient: ±0.8 ppm C -1 (-55 C to 85 C) Power ratin: C 1

10 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) 3. Measurement Concepts Fiure 2-1. Schematic Measurin strain is measurin a chane in lenth. Specifically, the unit strain ( ε ) is the chane in lenth divided by the unstrained lenth ( ε = Δ / ), and thus is dimensionless. T + Δ T T P P + Δ Fiure 3-1. Strain definition As the subject is elonated in the lonitudinal direction, the material will be narrowed or thinned down in the transverse direction. The ratio of the transverse strain to the lonitudinal strain is known as the Poisson ratio (ν). ν = ΔT Δ T 3.1 This Poisson ratio is a known property for most materials and is used in some half bride strain and full bride strain circuits. Strain is typically reported in microstrain ( με ). Microstrain is strain expressed in parts per million, i.e.: a chane in lenth divided by one millionth of the lenth. A metal foil strain aue is a resistive element that chanes resistance as it is stretched or compressed. The strain aue is bonded to the object in which strain is measured. The aue factor, F, is the ratio of the relative chane in resistance to the chane in strain: F = Δ / Δ l / l. For example, a aue factor of 2 means that if the lenth chanes by one micrometer per metre of lenth ( 1με ), the resistance will chane by two micro-ohms per ohm of resistance. A more common method of portrayin this equation is: 2

11 User Manual Or in terms of micro-strain: ε = με = Δ F 6 ( 1 10 ) Δ F Because the actual chane in resistance is small, a full Wheatstone bride confiuration is used to ive the maximum resolution. The Wheatstone bride can be set up with 1 active aue (Quarter bride strain circuit), two active aues (Half bride strain circuit), or 4 active aues (Full bride strain circuit). For each of these Wheatstone bride circuits there are multiple confiurations. The 4WFBS module provides three resistors that can be used for three of the arms of the Wheatstone Bride (Fiure 4-1). There are two 1000 ohm precision resistors for the back plane of the Wheatstone bride, and a resistor matchin the strain aue's resistance for the bride arm opposite the aue. The inputs of the 4WFBS are confiured so that this matchin resistor can be bypassed if it is desired to utilize a dummy aue, or to use two active aues (Half Bride Strain circuit). For Full Bride Strain circuits, as all four arms of the Wheatstone bride are active aues, there is no need for completion resistors, and thus a 4WFBS module is not required. The resistance of an installed aue will differ from the nominal value. In addition, lead resistance imbalances can result in further unbalancin of the bride. A zero measurement can be made with the aue installed. This zero measurement can be incorporated into the dataloer proram such that subsequent measurements can report strain relative to this zero basis point. This removes the apparent strain resultin from the initial bride imbalance. Strain is calculated in terms of the result of the full bride measurement. This result is the measured bride output voltae divided by the bride excitation voltae: V / V. out ex All of the various equations that are used to calculate strain use V r, the chane in the bride measurement from the zero state: V = ( V / V ) ( V / V ) r out ex Strained out ex Zero Quarter Bride Strain The result of the zero measurement, ( V out / V ex ) Zero, can be stored and used in the calculation of future strain measurements. Alternatively, the zero readin value can be left at 0 (zero measurement is neither recorded nor used). It should be noted the actual result of the full bride instruction (BrFull) is the millivolts output per volt of excitation (1000 Vout / Vex). The StrainCalc function used in CBasic uses this raw output as its input to calculate µstrain. See Section 4.5 Calculation of Strain for ¼ Bride Circuits for a detailed derivation of the equations used. A "quarter bride strain circuit" is so named because an active strain aue is used as one of the four resistive elements that make up a full Wheatstone bride. The 3

12 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) other three arms of the bride are composed of inactive elements. There are various circuits that use a sinle active element, includin 2-Wire aues, 3-Wire aues, as well as a few circuits that utilize a dummy aue for the arm opposite the arm holdin the active aue instead of a resistor, D in Fiure (See Fiures 4.3-1, 4.3-2, and 4.3-3). The 4WFBS TIM modules can support all types of these ¼ Bride Strain circuits. 4.1 Quarter Bride Strain with 3 Wire Strain Element A 3-wire quarter bride strain circuit is shown in fiure Strain aues are available in nominal resistances of 120, 350, and 1000 ohms. The 4WFBSXXX model must match the nominal resistance of the aue when usin the 3-Wire circuit (e.., the 4WFBS120 is used with a 120 ohm strain aue). In Fiure 4.1-1, 1 and 2 are 1000 ohm resistors makin up the back plane of the Wheatstone bride, as is done in the TIM desin. D, the third resistive element, is the complementary resistor that has a nominal resistance of the un-strained aue. The 4 th resistive element is the active strain aue. 2 =1 KΩ D Excite V = aue 1 =1 KΩ 2 1 Fiure Three wire quarter bride strain circuit The 3-Wire aue alleviates many of the issues of the 2-Wire aue. As can be seen in Fiure 4.1-1, lead wire 3 is in the arm of the Wheatstone bride that has the completion resistor while lead wire 1 is in the arm that has the active aue. 2 is tied back to the input channel of the dataloer that has an input resistance reater than 1 ohm, thus the current flow is neliible, neatin effects of 2 s resistance. This circuit nulls temperature induced resistance chanes in the leads as well as reduces the sensitivity effect that the wires have on the aue. See Section 4.4 for more on ead resistance effects and methods to compensate for them Quarter Bride Strain with 3 Wire Element Wirin Fiure illustrates the wirin of the strain aue to the 4WFBS module and the wirin of the module to the dataloer. It is important that the aue be wired as shown, and that the leads to the and terminals be the same lenth, diameter, and wire type. It is preferable to use a twisted pair for these two wires so that they will undero the same temperature and electromanetic field variations. With this confiuration, chanes in wire resistance due to temperature occur equally in both arms of the bride with neliible effect on the output from the bride. 4

13 1 N O User Manual Dataloer VX or EX 4WFBSXXX TIM Shunt eceptacle H A 2 =1KΩ 1=1KΩ D Active aue or Shunt eceptacle Fiure wire ¼ bride strain wirin Quarter Bride Strain with 3 Wire Element Wirin usin a multiplexer When usin a mechanical relay multiplexer such as the AM16/32B, the 4WFBS module should normally be placed on the face of the multiplexer similar as shown in Fiure WFBS AM16/32B elay Multiplexer H H H H H ES CK ND 12V 4X16 COM 7 EVEN ODD 13 H H H 2X32 C10X C23X C1000 C3000 C X C7 C800 C H H H H H A E1 E3 EX1 EX4 EX1 EX3 or VX1 VX4 VX1 VX3 EXCITATION SWITCHED EX1 EX2 or 1 4 ANAO OUT VX10VX H 1H 1H 1H 1H 1H 1H C800 C850 C10X C1000 C3000 C23X C X C7 Cable Shield 12 V 12 V 12 V +12 V 12 V C1 C4 C1 C8 C1 C8 EXCIT 1 4 EXCITATION C1 C4 C1 C8 C1 C8 C1 C6 725 Card Control Fiure wire ¼ bride strain with multiplexer wirin Althouh this requires a 4WFBS module for each strain aue, it is important because placin relays internal a Wheatstone bride strain system is discouraed. Any chane in resistance of the multiplexer s relay contacts would result in a correspondin chane in the bride s output voltae. Chanes in contact resistance can be induced by temperature fluctuations, oxidation, environmental conditions, and normal wear of contact surfaces. The specification for the relays that are used in our multiplexers state that initial contact resistance will be less than 100 milliohms (AM16/32B). There is not a specification for chane in contact resistance for the relays because there are so many variables that affect contact resistance. Test reports exist for various test conditions that show contact resistance chanin over time by 10 to 20 milli- Ohms. These tests were performed usin static test temperatures, so it is safe to assume that real world conditions would result in larer resistance shifts. 5

14 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) When strain aues are used in the Wheatstone bride, small chanes in contact resistance result in lare apparent strains. To understand the error that can be introduced from allowin the relay contacts to be internal of the Wheatstone bride, let us assume that the two relays carryin the current from the strain aue vary by 20 milliohms (40 milliohm total variance or Δ = 40 mω ). Insertin this into equation 3.3, usin a 120 ohm strain aue with a aue factor of 2 results in an apparent strain of about 167 με. 167με = 6 ( 1 10 ) 0.04Ω 2 120Ω Quarter Bride Strain with 3 Wire Element Calculations As noted in Section 3, in real life applications the Wheatstone bride starts out unbalanced. The strain aue is never perfectly at its nominal resistance even prior to installation. The installation process can lead to even more deviation from this nominal state. In addition, lead resistance can cause an initial apparent strain readin. To remove this initial offset, a zero measurement can be made with the aue installed. This zero measurement can be incorporated into the dataloer proram and subsequent measurements can report strain relative to this zero basis point. Strain is calculated in terms of the result of the full bride measurement. This result is the measured bride output voltae divided by the bride excitation voltae Vout / Vex. (The actual result of the full bride instruction is the millivolts output per volt of excitation, 1000 Vout / Vex) The result of the zero measurement, 1000 Vout 0 / Vex can be stored and used to calculate future strain measurements. The chane in the full bride measurement from the zero state, V r, is used in the calculation of the strain. Vr = ( Vout / Vex ) ( Vout 0 / Vex ) Usin V r from equation 4.1.1, the strain is calculated usin equation ε = 4Vr F( 1 2Vr ) The calculations are covered in more detail in Section Quarter Bride Strain with 3 Wire Proram Examples This section is broken out into CBasic prorams and EDO prorams. These prorams are only to be used as examples. Besides addin additional measurement instructions, the prorams will need to have the scan and data storae intervals altered for actual applications. efer to the dataloer s manuals and/or the CBasic Editor s help files for detailed information on the proram instructions used as well as additional proram examples CBasic Prorammin Dataloers that use CBasic include our C800, C850, C1000, C3000, C5000, and C9000(X). CBasic uses the StrainCalc Instruction for calculatin strain from the output of different full bride confiurations: StrainCalc(Dest,eps,Source,BrZero,BrConfi,aueFactor,Poissonatio) Source is the variable holdin the current result from the full bride measurement 6

15 User Manual BrZero is the zero measurement; this parameter uses the results of a previous full bride measurement instruction when the aue is at the zero condition (multiplier=1, offset=0, mv/v) directly. BCode for the Bride Confiuration used with the 4WFBS module should be set to -1 for a quarter bride strain circuit. Enter the actual aue factor in the auefactor parameter. Enter 0 for the Poisson ratio parameter, which is not used with ¼ Bride strain circuits. Example Proram 4.1. C9000X ¼ bride Strain with 3 reps This example proram measures the output from the Wheatstone bride usin the BrFull instruction. The output from this instruction is input into the StrainCalc instruction in order to calculate the raw µstrain value. This proram does not use a zero offset readin. See Example Proram 4.2 for an example that performs a zero calibration. ' Proram name: STAIN.C9X Public StrainMvperV(3) : Units StrainMvperV = mv_per_v 'aw Strain dimensioned source Public Strain(3) : Units Strain = ustrain ustrain dimensioned source Public F(3) 'Dimensioned aue factor DataTable(STAIN,True,-1) DataInterval(0,0,0,100) CardOut(0,-1) Sample (3,Strain(),IEEE4) Sample (3,StrainMvperV(),IEEE4) EndTable 'Trier, auto size 'Synchronous, 100 lapses, autosize 'PC card, size Auto '3 eps, ustrain, esolution 3eps,Stain mvolt/volt, esolution 'End of table STAIN BeinPro 'Proram beins here F(1) = 2.1 : F(2) = 2.2 : F(3) = 2.3 'Initialize aue factors for Strain( ) 7

16 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) Scan(10,mSec,100,0) 'Scan once every 10 msecs, non-burst BrFull(StrainMvperV(),3,mV50,4,1,5,7,1,5000,True,True,70,100,1,0) StrainCalc(Strain(),3,StrainMvperV(),0,-1,F(),0) 'Strain calculation CallTable STAIN Next Scan 'oop up for the next scan SlowSequence Scan(1,Sec,0,0) Calibrate BiasComp Next Scan EndPro 'Slow sequence Scan to perform temperature ' compensation on DAQ 'Corrects ADC offset and ain 'Corrects ADC bias current 'Proram ends here Example Proram 4.2. C9000X ¼ bride Strain with 3 reps and zero offset This example proram starts out with Example Proram 4.1 and adds instructions (hihlihted) to perform a zero calibration. As all strain circuits have a zero or initial imbalance that is related to the circuit rather than the member underoin strain, a zero readin is often used to offset or remove this apparent strain. Aain, see the manual and CBasic editor s Help file for more in-depth discussion on the instructions. The FieldCalStrain instruction takes care of the underlyin math for the zeroin usin equation The oadfieldcal instruction facilitates the reloadin of the calibration factors when the loer is powered up. In addition, the prorammer should create a DataTable (we have called this DataTable Calib in the example) to store the calibration factors each time a calibration is done. The NewFieldCal is a Boolean fla variable that is only hih durin the Scan that a calibration has been completed. It is used in the DataTable instruction s trier parameter to trier the table to record a record. The SampleFieldCal output instruction is used to inform the loer to store all of the calibration factors that are controlled usin the FieldCalStrain instruction. ' Proram name: STAIN0.C9X Public StrainMvperV(3) : Units StrainMvperV = mv_per_v 'aw Strain dimensioned source Public Strain(3) : Units Strain = ustrain ustrain dimensioned source Public F(3) 'Dimensioned aue factor Public ZeromV_V(3), ZeroStrain(3) Public Zeps, ZIndex, ModeVar DataTable(STAIN,True,-1) DataInterval(0,0,0,100) CardOut(0,-1) Sample (3,Strain(),IEEE4) Sample (3,StrainMvperV(),IEEE4) EndTable DataTable (Calib,NewFieldCal,10) SampleFieldCal EndTable 'Trier, auto size 'Synchronous, 100 lapses, autosize 'PC card, size Auto '3 eps, ustrain, esolution 3eps,Stain mvolt/volt, esolution 'End of table STAIN Table for calibration factors from zeroin User should collect these to his computer for future reference 8

17 User Manual BeinPro 'Proram beins here F(1) = 2.1 : F(2) = 2.2 : F(3) = 2.3 'Initialize aue factors for Strain( ) Zeps = 3 : ZIndex = 1 initialize cal reps and index pointer oadfieldcal(true) oad prior calibration factors Scan(10,mSec,100,0) 'Scan once every 10 msecs, non-burst FieldCalStrain(10,StrainMvperV(),Zeps,0,ZeromV_V(),ModeVar,0,ZIndex,1,0,Strain()) BrFull(StrainMvperV(),3,mV50,4,1,5,7,1,5000,True,True,70,100,1,0) StrainCalc(Strain(),3,StrainMvperV(),ZeromV_V(),-1,F(),0) 'Strain calculation CallTable STAIN CallTable Calib Next Scan 'oop up for the next scan SlowSequence Scan(1,Sec,0,0) Calibrate BiasComp Next Scan EndPro 'Slow sequence Scan to perform 'temperature compensation on the DAQ 'Corrects ADC offset and ain 'Corrects ADC bias current 'Proram ends here Example Proram 4.3. C1000 ¼ Bride Strain with 3 reps and zero offset This example proram performs the same tasks as Example Proram 4.2, only it is a C1000 proram instead of a C9000X proram. There are sliht differences such as rane codes and the fact that the C1000 does not have a Slot parameter for its measurement instructions. This proram is more similar to what a C800, C3000, or a C5000 proram would look like than the C9000X proram. ' Proram name: STAIN0.C1 Public StrainMvperV(3) : Units StrainMvperV = mv_per_v 'aw Strain dimensioned source Public Strain(3) : Units Strain = ustrain ustrain dimensioned source Public F(3) 'Dimensioned aue factor Public ZeromV_V(3), ZeroStrain(3) Public Zeps, ZIndex, ModeVar DataTable(STAIN,True,-1) DataInterval(0,0,0,100) CardOut(0,-1) Sample (3,Strain(),IEEE4) Sample (3,StrainMvperV(),IEEE4) EndTable DataTable (Calib,NewFieldCal,10) SampleFieldCal EndTable 'Trier, auto size 'Synchronous, 100 lapses, autosize 'PC card, size Auto '3 eps, ustrain, esolution 3eps,Stain mvolt/volt, esolution 'End of table STAIN Table for calibration factors from zeroin User should collect these to his computer for future reference BeinPro 'Proram beins here F(1) = 2.1 : F(2) = 2.2 : F(3) = 2.3 'Initialize aue factors for Strain( ) Zeps = 3 : ZIndex = 1 initialize cal reps and index pointer oadfieldcal(true) oad prior calibration factors Scan(100,mSec,100,0) 'Scan once every 10 msecs, non-burst FieldCalStrain(10,StrainMvperV(),Zeps,0,ZeromV_V(),ModeVar,0,ZIndex,1,0,Strain()) BrFull(StrainMvperV(),3,mV7_5,1,1,3,2500,True,True,450,500,1,0) StrainCalc(Strain(),3,StrainMvperV(),ZeromV_V(),-1,F(),0) 'Strain calculation CallTable STAIN CallTable Calib Next Scan 'oop up for the next scan 9

18 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) Example Proram 4.3. C1000 ¼ Bride Strain usin an AM16/32B Multiplexer with 16 reps and zero offset This example proram has 16 strain aues multiplexed throuh an AM16/32 Multiplexer and uses FieldCalStrain for zeroin. ' Proram name: QuarterStrain with Zero and Mux.C1 ' This is only an example proram and should be used only for help in creatin a usable proram ' WIIN ' C1000 to AM16/32 Multiplexer Control ' C1 (Control Port 1) es (eset) ' C2 (Control Port 2) Clk (Clock) ' ND (round) ' 12V 12V ' C1000 to AM16/32 Common TIMs to AM16/32 Banks ' Diff 1H to Common Even Hi Blk Wire to Bank Odd o ' Diff 1 to Common Even o TIM H to Bank Even Hi ' EX1 to Common Odd o Tim to Bank Even o ' A to Common nd Tim A to Bank Even A '\\\\\\\\\\\\\\\\\\\\\\\DECAE VAIABES and CONSTANTS /////////////////////// Const EPS = 16 'Strain aue sensor count Public MVpV(EPS) : Units MVpV = mv_v 'mv per Volt output from Bride Measurement Public STAIN(EPS) : Units STAIN = ustrain 'Variable where us is stored, Const BATCH_F = 2.1 : Public F(EPS) 'Batch aue Factor Public mv_vzero(eps) : Units mv_vzero = mv_v 'Variable for Zero mv per V readin Public Caleps, ZeroMode, ZeroStartIdx, ZeroCalAvs 'Used by wizard for zeroin Public CalFileoaded As Boolean Dim I '\\\\IF DESIED (NOT EQUIED): IVE STAIN VAIABES UNIQUE AIAS NAMES //////// Alias STAIN(1) = Strain1 : Alias STAIN(2) = Strain2 : Alias STAIN(3) = Strain3 Alias STAIN(4) = Strain4 : Alias STAIN(5) = Strain5 : Alias STAIN(6) = Strain6 Alias STAIN(7) = Strain7 : Alias STAIN(8) = Strain8 : Alias STAIN(9) = Strain9 Alias STAIN(10) = Strain10 : Alias STAIN(11) = Strain11 : Alias STAIN(12) = Strain12 Alias STAIN(13) = Strain13 : Alias STAIN(14) = Strain14 : Alias STAIN(15) = Strain15 Alias STAIN(16) = Strain16 '\\\\\\\\\\\\\\\\\\\\\\\\ OUTPUT SECTION //////////////////////// ' Table STAIN stores ustrain and raw mv per Volt measurements to the PC Card DataTable(STAIN,True,-1) 'Trier, auto size DataInterval(0,0,0,100) 'Synchronous, 100 lapses CardOut(0,-1) 'PC card, Autosize Sample (EPS,STAIN(),IEEE4) 'Sample ustrain Sample (eps,mvpv(),ieee4) 'Sample raw mv per Volt values EndTable 'End of table ' Table CalHist uses SampleFieldCal which stores all of the Calibration constants ' When a calibration function is complete, user should always collect this Table as a record DataTable(CalHist,NewFieldCal,50) SampleFieldCal EndTable '\\\\\\\\\\\\\\\\\\\\\\\\MAIN POAM SECTION //////////////////////// BeinPro 'Proram beins here For I = 1 To EPS ' For the 16 aues F(I) = BATCH_F 'Assin default aue factor (2.1) to F array elements Next I 'oop back up until complete CalFileoaded = oadfieldcal(1) 'oad the Cal constants if proram sinature matches 10

19 User Manual Scan(1,Sec,10,0) 'Scan once a Second PortSet (1,1 ) 'Turn on AM16/32 usin C1 I = 1 Delay (0,150,mSec) 'required Delay for AM16/32 multiplexer SubScan (0,0,16) PulsePort (2,10000) 'Pulse port C2 hi and low to clock the multiplexer BrFull(MVpV(I),1,mV7_5C,1,VX1,1,2500,True,True,250,500,1,0) 'Full Bride measurement StrainCalc(Strain(I),1,MVpV(I),mV_VZero(I),-1,F(I),0) 'Strain calculation I = I + 1 'Increment I NextSubScan PortSet (1,0 ) 'Turn on AM16/32 usin C1 FieldCalStrain(10,MVpV(),Caleps,0,mV_VZero(),ZeroMode,0,ZeroStartIdx,ZeroCalAvs,0,STAIN()) CallTable CalHist CallTable STAIN Next Scan 'oop up for the next scan EndPro 'Proram ends here Edlo The followin examples for the C10(X), 21X, and C7 all have subroutines that measures the unstrained "zero" output of the strain aue. The examples calculate strain usin equation for a strain aue with a F=2. These are just examples. Besides addin additional measurement instructions, the prorams will probably need to have the scan and data storae intervals altered for actual applications. The instructions in the subroutine will also need to be modified for the actual aue factor. Dataloers that use Edlo include C510, C10(X), 21X, and C7. The Edlo instruction that is used to measure strain aues is Instruction 6 Full Bride. The Input ocations assinments used in C10(X), 21X, and C7 Examples are listed in Table 4-1. Table 4-1. Input ocations Used in C10(X), 21X, and C7 Examples Addr Name 1 mvperv 2 mvperv_0 3 Vr 4 ustrain 5 Count 6 F 7 _4e6 8 Mult 9 1_2Vr 10 Vr_1_2Vr 11

20 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) Example Proram 4.4. C10X ¼ Bride Strain with 1 rep and zero offset ;{C10X} *Table 1 Proram 01: 1 Execution Interval (seconds) 1: If Fla/Port (P91) ;On the first execution (Fla 1 is low) 1: 21 Do if Fla 1 is ow ;or when user sets Fla 1 low 2: 1 Call Subroutine 1 ;call the zeroin subroutine 2: Full Bride (P6) ;Measure the strain aue 1: 1 eps 2: 22 ± 7.5 mv 60 Hz ejection ane 3: 1 DIFF Channel 4: 1 Excite all reps withexchan 1 5: 2500 mv Excitation 6: 1 oc [ mvperv ] 7: 1 Mult 8: 0 Offset 3: X-Y (P35) ;Subtract zero readin from the 1: 1 X oc [ mvperv ] ;measurement 2: 2 Y oc [ mvperv_0 ] 3: 3 Z oc [ Vr ] 4: X*F (P37) ;Chane Vr from mv/v to V/V 1: 3 oc [ Vr ] 2: : 3 oc [ Vr ] ;The followin instructions calculate microstrain 5: Z=X*F (P37) 1: 3 X oc [ Vr ] 2: -2 F 3: 9 Z oc [ 1_2Vr ] 6: Z=Z+1 (P32) 1: 9 Z oc [ 1_2Vr ] 7: Z=X/Y (P38) 1: 3 X oc [ Vr ] 2: 9 Y oc [ 1_2Vr ] 3: 10 oc [ Vr_1_2Vr ] 8: Z=X*Y (P36) 1: 10 X oc [ Vr_1_2Vr ] 2: 8 Y oc [ Mult ] 3: 4 Z oc [ ustrain ] ; Output Section : This example outputs an averae of the 1 second readins ;once per minute. 09: If time is (P92) 1: 0 Minutes (Seconds --) into a 2: 1 Interval (same units as above) 3: 10 Set Output Fla Hih 10: Set Active Storae Area (P80) 1: 1 Final Storae Area 1 2: 1 Array ID ;Set Array ID = 1 for measurement data 11: eal Time (P77) 1: 1110 Year,Day,Hour/Minute 12

21 User Manual 12: Averae (P71) 1: 1 eps 2: 4 oc [ ustrain ] *Table 2 Proram 2: Execution Interval (seconds) *Table 3 Subroutines 1: Beinnin of Subroutine (P85) ;Subroutine to measure "zero" 1: 1 Subroutine 1 2: Do (P86) ;This prevents callin subroutine 1: 11 Set Fla 1 Hih ;until user sets fla 1 low aain. 3: Z=F (P30) ;Set counter use for averae to 0 1: 0 F 2: 0 Exponent of 10 3: 5 Z oc [ Count ] 4: Z=F (P30) ;load 4 million (4*uS/S) into input location 1: 4 F 2: 6 Exponent of 10 3: 7 Z oc [ _4e6 ] 5: Z=F (P30) ;oad aue Factor into input location 1: 2 F ;Enter the actual aue Factor here 2: 0 Exponent of 10 3: 6 Z oc [ F ] 6: Z=X/Y (P38) ;calculate multiplier to use with strain 1: 7 X oc [ _4e6 ] ;calculation 2: 6 Y oc [ F ] 3: 8 Z oc [ Mult ] 7: Beinnin of oop (P87) ;oop throuh 5 times to obtain averae 1: 0 Delay ;zero readin 2: 5 oop Count 8: Z=Z+1 (P32) ;Increment Counter used to determine 1: 5 Z oc [ Count ] ;when to output 9: Full Bride (P6) ;Measure Strain aue 1: 1 eps 2: 22 ± 7.5 mv 60 Hz ejection ane 3: 1 DIFF Channel 4: 1 Excite all reps withexchan 1 5: 2500 mv Excitation 6: 1 oc [ mvperv ] 7: 1 Mult 8: 0 Offset 10: IF (X<=>F) (P89) ;Check for last pass throuh loop 1: 5 X oc [ Count ] ;to set output fla 2: 3 >= 3: 5 F 4: 10 Set Output Fla Hih 11: Set Active Storae Area (P80) ;Direct averaed "zero" readin 1: 3 Input Storae Area ;to input storae 2: 2 Array ID or oc [ mvperv_0 ] 12: Averae (P71) 1: 1 eps 2: 1 oc [ mvperv ] 13: If Fla/Port (P91) ;When averae is calculated, 13

22 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) 1: 10 Do if Output Fla is Hih (Fla 0) ;also send it to Final Storae 2: 10 Set Output Fla Hih 14: Set Active Storae Area (P80) ;Direct Output to Final Storae 1: 1 Final Storae Area 1 2: 11 Array ID ;set Array ID = 11 for zero data 15: eal Time (P77) 1: 110 Day,Hour/Minute 16: Sample (P70) 1: 1 eps 2: 2 oc [ mvperv_0 ] 17: End (P95) 18: End (P95) End Proram Example Proram X ¼ Bride Strain with 1 rep and zero offset ;{21X} *Table 1 Proram 01: 1 Execution Interval (seconds) ;Other measurements could be inserted here or before the Output section 1: If Fla/Port (P91) ;On the first execution (Fla 1 is low) 1: 21 Do if Fla 1 is ow ;or when user sets Fla 1 low 2: 1 Call Subroutine 1 ;call the zeroin subroutine 2: Full Bride (P6) ;Measure the strain aue 1: 1 eps 2: 2 ± 15 mv Slow ane 3: 1 DIFF Channel 4: 1 Excite all reps withexchan 1 5: 5000 mv Excitation 6: 1 oc [ mvperv ] 7: 1 Mult 8: 0 Offset 3: Z=X-Y (P35) ;Subtract zero readin from the 1: 1 X oc [ mvperv ] ;measurement 2: 2 Y oc [ mvperv_0 ] 3: 3 Z oc [ Vr ] 4: Z=X*F (P37) ;Chane Vr from mv/v to V/V 1: 3 X oc [ Vr ] 2: F 3: 3 Z oc [ Vr ] 14

23 User Manual ;The followin instructions calculate microstrain 5: Z=X*F (P37) 1: 3 X oc [ Vr ] 2: -2 F 3: 9 Z oc [ 1_2Vr ] 6: Z=Z+1 (P32) 1: 9 Z oc [ 1_2Vr ] 7: Z=X/Y (P38) 1: 3 X oc [ Vr ] 2: 9 Y oc [ 1_2Vr ] 3: 10 Z oc [ Vr_1_2Vr ] 8: Z=X*Y (P36) 1: 10 X oc [ Vr_1_2Vr ] 2: 8 Y oc [ Mult ] 3: 4 Z oc [ ustrain ] ;Output Section ;This example outputs an averae of the 1 second readins ;once per minute. 9: If time is (P92) 1: 0 Minutes (Seconds --) into a 2: 1 Interval (same units as above) 3: 10 Set Output Fla Hih 10: Set Active Storae Area (P80) 1: 1 Final Storae Area 1 2: 1 Array ID ;Set Array ID = 1 for measurement data 11: eal Time (P77) 1: 1110 Year,Day,Hour/Minute 12: Averae (P71) 1: 1 eps 2: 4 oc [ ustrain ] *Table 2 Proram 01: Execution Interval (seconds) *Table 3 Subroutines 1: Beinnin of Subroutine (P85) ;Subroutine to measure "zero" 1: 1 Subroutine 1 2: Do (P86) ;This prevents callin subroutine 1: 11 Set Fla 1 Hih ;until user sets fla 1 low aain. 3: Z=F (P30) ;Set counter use for averae to 0 1: 0 F 2: 5 Z oc [ count ] 4: Z=F (P30) ;load 4000 into 1: 4000 F ;input location 2: 7 Z oc [ 4e6 ] 5: Z=X*F (P37) ;Multiply by 1000 to et (4*uS/S) 1: 7 X oc [ 4e6 ] 2: 1000 F 3: 7 Z oc [ 4e6 ] 6: Z=F (P30) ;oad aue Factor into input location 1: 2 F ;Enter the actual aue Factor here 2: 6 Z oc [ F ] 7: Z=X/Y (P38) ;calculate multiplier to use with strain 15

24 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) 1: 7 X oc [ 4e6 ] ;calculation 2: 6 Y oc [ F ] 3: 8 Z oc [ Mult ] 8: Beinnin of oop (P87) ;oop throuh 5 times to obtain averae 1: 0 Delay ;zero readin 2: 5 oop Count 9: Z=Z+1 (P32) ;Increment Counter used to determine 1: 5 Z oc [ count ] ;when to output 10: Full Bride (P6) ;Measure Strain aue 1: 1 eps 2: 2 ± 15 mv Slow ane 3: 1 DIFF Channel 4: 1 Excite all reps withexchan 1 5: 5000 mv Excitation 6: 1 oc [ mvperv ] 7: 1 Mult 8: 0 Offset 11: IF (X<=>F) (P89) ;Check for last pass throuh loop 1: 5 X oc [ count ] ;to set output fla 2: 3 >= 3: 5 F 4: 10 Set Output Fla Hih 12: Set Active Storae Area (P80) ;Direct averaed "zero" readin 1: 3 Input Storae ;to input storae 2: 2 Array ID or oc [ mvperv_0 ] 13: Averae (P71) 1: 1 eps 2: 1 oc [ mvperv ] 14: If Fla/Port (P91) ;When averae is calculated, 1: 10 Do if Output Fla is Hih (Fla 0) ;also send it to Final Storae 2: 10 Set Output Fla Hih 15: Set Active Storae Area (P80) ;Direct Output to Final Storae 1: 1 Final Storae 2: 11 Array ID ;set Array ID = 11 for zero data 16: eal Time (P77) 1: 110 Day,Hour/Minute 17: Sample (P70) 1: 1 eps 2: 2 oc [ mvperv_0 ] 18: End (P95) 19: End (P95) End Proram 16

25 User Manual 4.2 Quarter Bride Strain with 2 Wire Element NOTE Althouh a two wire aue can be used with the 4WFBS TIM, due to the issues outlined in Section 4.4.3, it is not recommended. An exception may be applications with short leads in a stable temperature environment. A 2-wire quarter bride strain circuit is shown in fiure =1KΩ D Excite V =aue 1 =1KΩ Fiure Two wire quarter bride strain circuit In this circuit, 1 and 2 are 1000 ohm resistors makin up the back plane of the Wheatstone bride, as is done in the TIM desin. D is the complementary resistor, or Dummy esistor, that has a nominal resistance of the un-strained aue. The 4 th resistive element is the active strain aue. Strain aues are available in nominal resistances of 120, 350, and 1000 ohms. The 4WFBS model must match the nominal resistance of the aue (e.., the 4WFBS120 is used with a 120 ohm strain aue). As can be seen in Fiure 4.2-1, both sensor leads are in the same arm of the Wheatstone bride. Not only does this affect the sensitivity of the aue, the output from this circuit will include temperature induced line resistance errors. See Section 4.4.3, ead Compensation usin ¼ Bride Strain with 2 Wire Element for more information on issues with usin 2 wire aues Quarter Bride Strain with 2 Wire Element Wirin To use a two wire element strain aue with the 4WFBS TIM requires a jumper wire be placed between the H and terminal of the TIM module as shown in Fiure

26 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) Dataloer Vx H H Jumper Wire 2 D or A 1 aue or Shield Fiure Wirin for 2-wire aues Two Wire ¼ Bride use with Multiplexers and Equations The equations to resolve the strain, prorammin of the loer, and methods of usin with multiplexers are the same as those covered in Section 4.1 for the 3- Wire Strain aue. The only variance is the wirin of the aue to the TIM. 4.3 Quarter Bride Strain with Dummy aue An undesirable property of strain aues is that of resistance chane with chanes in temperature. This is true even for the self-temperature compensatin strain aues on the market today. Supplied with each packae of strain aues are raphs and equations for the variance in the output of the strain aue due to thermal chanes (referred to as thermal output or apparent strain) and for the variation of the aue factor with temperature. These raphs are based on the assumption that the aues are mounted on a material with the iven thermal coefficient of expansion (TCE). The TCE value is included in the aue type nomenclature. Followin are some typical equations supplied. Equation is used to calculate the thermal output variance (µε TO ) with the result in μstrain. Equation is used to determine the chane in the aue factor (F) due to temperature chanes. Both are based on temperature in derees Celsius (T). με TO = T 0.05T E T 3.93E T adj raw ( T ) Fraw 4 F = F E As an example, let us assume we use a aue with a F of 2.00 in a test that started at 24 C and 0 μstrain, and ended at 50 C and a recorded strain value of 1000 μstrain. The thermal output strain, µε TO, at 50 C would be μstrain. The error in the aue factor would be 0.364% with a resultant F adj of The corrected strain would be 967 μstrain: ( 1000 με 29.3 ) / με cor = με The uncorrected value had an error of approximately 3.3%. And if the endin strain would have been 100 μstrain instead of 1000 μstrain, the error would have been around 30%. Another temperature induced error in a quarter bride strain circuit is due to the Temperature Coefficient of esistance (TC) of the completion resistor in the arm opposite the strain aue. The 4WFBS TIMs use a hih quality resistor havin a TC of 0.8ppm/ C to minimize these errors. For our example above, this could lead to an error in the readin of approximately 10 μstrain, assumin that the dataloer experiences the same level of temperature variation. This error could 18

27 User Manual be additive or subtractive to the other errors as the resistor manufacturer does not specify the polarity of the chane in resistance, only the absolute manitude. These errors, with exception to the completion resistor s TC, can be mathematically compensated for to some deree. It should be remembered that the curves and equations iven are the averae for the iven batch of aues and are only applicable when mountin on the specified material. An alternative approach to eliminate the errors is to either use a dummy aue, from the same batch mounted on identical material, or to use a half or full bride strain circuit. Dummy aues can be used to compensate for these false apparent strain readins. A strain aue that is mounted on a coupon that is not underoin mechanical stress and is used as the resistive element for the Wheatstone bride arm opposite the active aue is referred to as a Dummy aue. This non-active aue in the other arm of the Wheatstone bride is referred to as a dummy aue because it is not subjected to load induced strains. With the two opposin aues experiencin the same temperature conditions, the temperature effects on the active aue will be nullified by the equivalent temperature effects on the dummy aue. Fiure depicts a Quarter Bride Strain circuit with a Dummy aue. 2 =1 KΩ 3 3 Dummy aue =1 KΩ 1 Active aue Fiure Quarter bride strain circuit with dummy aue It should be noted that the coupon on which the dummy aue is mounted can still be subjected to temperature induced strains. This can be used to null temperature induced strains in the monitored member if the dummy aue is mounted to a coupon made up of material havin the same Temperature Coefficient of esistance (TC) as the member that the active aue is mounted to. Conversely, the dummy aue could be mounted to a coupon with a neliible TC allowin for the monitorin of temperature induced stresses. The 4WFBS modules can support quarter bride strain circuits usin either the completion resistor built into the TIM, or a user supplied dummy strain aue, for the Wheatstone Bride arm's resistive element opposite of the active strain aue in the bride. Wirin circuits usin a dummy aue are covered in Section Quarter Bride Strain with Dummy aue Wirin Setup Fiure illustrates the wirin of the strain aue with a dummy aue to the 4WFBS module, as well as the wirin of the module to the dataloer. This shows the dummy aue out at the remote site alon with the active aue. This is the best setup to achieve the best compensation for the apparent strain and 19

28 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) aue factor variance due to temperature fluctuations, as it will be easier to keep the temperature of the two aues equivalent. Fiure ¼ bride strain with remote dummy aue Fiure illustrates the wirin of the strain aue to the 4WFBS module with the Dummy aue at the loer location. Apparent strain errors could result because of temperature variances between the two aues with this setup. This circuit is still utilized in some applications for ease of Shunt calibration (can shunt across Dummy aue at loer location rather than at the remote aue location). Also an existin, standard 3-wire ¼ Bride strain circuit can easily be transformed into this circuit. If lare temperature variances will exist between the active aue and the dummy aue located at the dataloer, usin the 4WFBS completion resistor can result in lower temperature induced errors. Fiure ¼ bride strain with dummy aue at dataloer With either circuit, one lead le, 1 or 3, is in one of the two opposin arms of the Wheatstone bride. It is important that the aue be wired such, and that these two leads be the same lenth, diameter and wire type. It is preferable to use a twisted pair for these two wires so that they will undero the same temperature and electromanetic field variations. With this confiuration, chanes in wire resistance due to temperature occur equally in both arms of the bride with neliible effect on the output from the bride Quarter Bride Strain with Dummy aue Calculations The calculations for this bride setup are the same as for the 3-Wire Quarter Bride circuit. See Section Quarter Bride Strain with3 Wire Element Calculations for details. 20

29 User Manual Quarter Bride Strain with Dummy aue Example Prorams The prorammin for this bride setup is the same as for the 3-Wire Quarter Bride circuit. See Section Quarter Bride Strain with3 Wire Proram Examples for details. 4.4 Quarter Bride Strain ead esistance Compensation When usin quarter bride strain (full bride with one active element) with lon lead lenths, errors can be introduced due to the resistance of the leads. This section covers both mathematical and Shunt Calibration methods used to rectify these errors. The techniques covered in the section can be used with circuits usin a 4WFBS s completion resistor or a dummy aue for the resistive element in the third arm of the Wheatstone Bride (arm opposite of active aue). The only difference is that when usin a dummy aue, the 4WFBS module s old shunt receptacles cannot be used. These receptacles are connected to the dummy resistor supplied by the 4WFBS module. One potential error with lon leads is due to the leads' resistance chane from temperature fluctuations. When usin a three wire strain aue, wired as depicted in Fiure Wire ¼ Bride Strain Wirin, with the three leads all the same lenth and laid out toether (all three experience the same temperature swins), the leads' resistance chanes are self compensatin. It is preferable to use a twisted pair for the two wires ( and ) carryin the current so that they definitely undero the same temperature and electromanetic field variations. With this confiuration, chanes in wire resistance due to temperature occur equally in both arms of the bride with neliible effect on the output from the bride. Another error that is introduced when usin lon leads, is a sensitivity reduction of the system. There are two methods to rectify this error. The first is mathematical. The second is to perform a shunt calibration. Sections and cover these methods for ¼ Bride Strain circuits Mathematical ead Compensation for 3-Wire, ¼ Bride Strain The same equations pertain whether a completion (dummy) resistor or a dummy aue is used to complete the third arm of the Wheatstone Bride. So the material in this section is relevant for wirin setups shown in Fiures 4.1-2, 4.3-2, and The math and the prorams used would be identical for all three of these circuits Mathematical ead Compensation Circuit and Equations If the lead resistance is known, the sensitivity error can be mathematically corrected for by multiplyin the output by a simple factor (1+ / ) where is the nominal resistance of one of the lead les and is the resistance of the strain aue. The aue Factor can be multiplied by the inverse of this value, /( + ), to derive an adjusted aue Factor. F adj = F raw The adjusted aue Factor, F adj, would be used in the StrainCalc function to derive the µstrain. The proof used to derive this adjusted aue Factor is shown below: 21

30 4WFBS120, 4WFBS350, 4WFBS1K 4 Wire Full Bride Terminal Input Modules (TIM) 22 2 = 1KΩ 1 = 1KΩ D 4 =aue Excite + - Fiure Three wire ¼ bride strain circuit Balanced Bride Condition D BA I O E E = Strained Bride Condition D ST I O E E + + Δ Δ + = Chane in Bride Output (V ) D D BA I O ST I O 2 2 E E E E V Δ Δ + = = 4.4.4

31 User Manual Assume D = V + + Δ = Δ Simplify V = ( Δ )( ) Δ + Δ Solve for Δ / Δ = 4V + ( 1-2V ) Δ 10 Use the aue Factor to calculate micro-strain με = F 4V με = F ( 1-2V ) Mathematical ead Compensation Prorams Example Proram 4.6. C9000X ¼ Bride Strain with zero offset and ead Compensation This proram starts with Example Proram 4.2 and adds instructions to mathematically compensate for the leads resistances effects on the aue Factor (sensitivity effect). Added instructions are hihlihted. ' Proram name: StrainSH.C9X Public StrainMvperV(3) : Units StrainMvperV = mv_per_v 'aw Strain dimensioned source Public Strain(3) : Units Strain = ustrain ustrain dimensioned source Dim F(3) 'Dimensioned aue factor Public ZeromV_V(3), ZeroStrain(3) Public Zeps, ZIndex, ModeVar Public eadlenth(3), ead_(3),f_adjusted(3), Public I, eadper100ft, aue_ DataTable(STAIN,True,-1) DataInterval(0,0,0,100) CardOut(0,-1) Sample (3,Strain(),IEEE4) Sample (3,StrainMvperV(),IEEE4) EndTable DataTable (Calib,NewFieldCal,10) SampleFieldCal EndTable 'Trier, auto size 'Synchronous, 100 lapses, autosize 'PC card, size Auto '3 eps, ustrain, esolution 3eps,Stain mvolt/volt, esolution 'End of table STAIN Table for calibration factors from zeroin User should collect these to his computer for future reference 23