Veerapong Kanchanawongkul*

Transcription

1 Using LabVIEW to Development of Temperature Measurement System with Thermocouple and Thermistor AIS 08 Veerapong Kanchanawongkul* Department of Mechanical Engineering, Faculty of Engineering, South-East Asia University, Bangkok, Thailand *Corresponding Author: Tel: (662) , Fax: (662) , Abstract Thermocouple and thermistor are two types of instruments used for recording temperature measurements and broadly used of temperature sensing devices. At present, the LabVIEW is efficiently used to easy implement a number of optimum measurements, which was developed by computer notebook connected with data acquisition (DAQ) device. It was a receiver of signal input transferred, from sensing devices of external testing set and particularly established to a very important research. However, results were observed and somewhat compared with the traditional temperature measurement device of the test that this temperature measurement system has the benefits of cost saving, easy operation, quick display, good precision and variable applications in engineering.. Keywords: temperature measurement system, thermocouple, thermistor, data acquisition (DAQ). Introduction The both of thermocouple and thermistor are two types of instruments are very rugged and generally used for recording temperature measurements due to inexpensive purchase and easy operations. Certainly, one of the most important activities in heat transfer is the measurements of temperature. It was largely measured in mechanical manufacturing or scientific experiments about the temperature of a surface, fluid or solid body will provide much of the information concerning the heat transfer processes at work. There are many methods to measure temperatures. These include, to mentions only a few is thermometers, thermocouples and thermistors, which development used thermocouples and thermistors as receiver of signal input. Due to effects of various development of modern technology for temperature measurement system are highly used in processes, but limited with high cost in specific operations, no capacity of program to measuring temperature and find damage of several instruments in operation. Thus, the investigation of temperature was to plan on development of temperature measurement system to measure in simple change temperatures. 834

2 It was tested with the hot plate as added heating of water and written by LabVIEW to use with instantaneous instruments, easy operation, quick display and good precision. Materials and Methods Thermocouple (Thermoelectric Sensor) Thermocouple is created whenever two dissimilar metals touch and the contact point produces a small open-circuit voltage as a function of temperature. This voltage of thermoelectric is known as the Seebeck voltage and named after Thomas Seebeck, who discovered it in 1821 [1]. The nonlinear voltage is varied by temperatures and small changes in temperature to approximate linear of voltage. A general equation can be written as [2]: ΔV = S ΔT (1) Where ΔV and ΔT are the changes in voltage and temperature, and then S is the Seebeck coefficient. A process of linearizing the data of thermocouple output voltages are highly nonlinear. The Seebeck coefficient can vary by a factor of three and more over the operating temperature range of some thermocouples. This reason, the graph line is created by approximate between the thermocouple voltage versus temperature curve which was plotted with polynomials type and it is in the following form: 2 n T = a + a V + a V a (2) nv Where V is the thermocouple voltage, T is the temperature (degrees Celsius) and a 0 to a n are coefficients that are specific values of each type of thermocouples [1]. The several types of thermocouples are available, and different types are designated by capital letters that indicate compositions of thermocouple types (B, E, J, K, N,, S and T types), which was determined to American National Standard Institute (ANSI). For this investigation, used a K-type thermocouple and fabricated with Nickel-chromium alloy (chromel) and Nickelaluminum alloy (alumel) [3] and then soldering the tip. Thermistor (Bulk Semiconductor Sensor) The thermistors are resistors, specially made from some type of semiconductor, which may be a semiconductor like Silicon, but more generally is a ceramic or plastic. There are two types of thermistors were produced to have a Positive Temperature Coefficient (PTC) and a Negative Temperature Coefficient (NTC), but various thermistors used for temperature measurement have a NTC [4]. For thermistors was produced with manganese, nickel, cobalt oxides are nonlinear. It was milled, mixed with binders, pressed into the desired shape, sintered and commercially produced in the form of beads, flakes, rods and disks. However, most temperature sensing implement are used to recording temperature measurements with probes and a computerized data system. [5] The using the thermistors to measure the temperature, is varied with temperatures. From the original equation of the resistance of a thermistor 835

3 at temperature T and indicate in the temperature form as a function of the resistance yields. Therefore, equation can be written as [5]: T 1 T 1 + ln B 1 = (3) Where is the resistance (10000 ohms) at a reference temperature T (273 K adds with an ambient temperature) and B is a constant value (4038 ± 10% tolerance on the resistance). Fig. 1 The voltage divider circuit Figure 1 shows the voltage divider circuit which was connected into the specific source of power supply (5 VDC) for the input voltage (V i ) and transfer the output voltage (V ) to the data acquisition (NI USB-6009). The output voltage can be written as: 1V (V - V = (5) i ) Inserting the resistance of the equation (5) into the equation (3) and result of the temperature as a function of voltage was conducted to the data acquisition. Therefore, equation can be written as: T V = + ln T B (Vi V (6) The general thermistors are limited and use measure temperature below about 130 C [4] or 288 C [3]. For this investigation, used a 10K ohm resistor of a thermistor and closed with a stainless steel housing and use to immerse in water. This reason, the water conducts diffuse and cause significant changes into the thermistor. Preparations and LabVIEW Programming Fig. 2 The front panel of LabVIEW programming V 2 Vi = (4) When 2 is the resistance of a thermistor and the resistance can be adjusted equation as: 836

4 Fig. 3 The block diagram of LabVIEW programming. Figure 2 shows the two parts of the front panel of LabVIEW programming to measure temperature with (a) the thermocouple and (b) the thermistor. The main components were indicated at the block diagram of each part in the front panel (Fig.2) such as the thermocouple temperature programming in Figure 3 and different on data acquisition (DAQ) of products. Figure 3 shows the total details of the block diagram, in which each data acquisition of products (1) NI USB-6009 and (2) ADAM 4018 was replaced with the signal input in block diagram and interface to comport (ADAM 4018). Figure 4 shows the two parts of some block diagram of LabVIEW programming to measure temperature with (a) the thermocouple and (b) the thermistor. For Thermistor, under the flat sequence of NI USB-6009 (DAQ Assist) was indicated in the voltage values and transferred to two parts of configure formula to take of temperature in degrees Fahrenheit ( F) and then adjusted to the degrees Celsius ( C). For Thermocouple, under the flat sequence of ADAM 4018 (Instr Assist) of string subset function was adjusted to numbers of fract/exp string to number function and indicated the degrees Celsius. In addition, for Figure 4 (a) shows the voltage values, which was calculated the interpolation range of a K-type thermocouple in formula node whereas suddenly shown the voltage values in Figure 4 (b) by without calculation, but must be used specific the formula to the correct values of calculation with equation (6). Fig. 5 Preliminary preparation results in the ambient of LabVIEW programming Fig. 4 Some block diagram of LabVIEW programming. Figure 3 shows the flat sequence under the case structure (right). There were the three values to the drive C and write in text file form, which were saved by the write to spreadsheet file (1D 837

5 data input). It was transferred to the case structure and for Loop operated and then partly saved with the format into file as shown in Figure 5. It was clearly found that more the vibrant amplitude of each temperature and voltage of the thermistor than the thermocouple and can be used to measure temperatures. The top of table was determined by format into file function, which was inserted both of the source type (ambient) and the indicator type (thermocouple or thermistor) of the front panel of LabVIEW programming and shown in Figure 3 of the left and under for Loop. and (c). For LabVIEW programming develops from LabVIEW 2011 (LabVIEW FULL DEVELPMENT SYSTEM), in which was used to investigation as simple change temperature. The first, the thermocouple and the thermistor is immersed into a cup of hot water as put on a hot plate. It was added with the electrical power and transferred a cup and then the temperatures of increasing water. The calibration temperature used reference temperature of laboratory room at 31 C and adjusted a temperature of front panel both of thermocouple and thermistor equal the reference temperature as operated program in figure 6(a) and then inserted into a source type and indicator type. It was saved into program to start operation and pressed the auto save of program and then temperatures will be saved in a specific file. esults and Discussions Fig. 6 Preparations and measuring temperature with thermocouple and thermistor Figure 6 shows the experimental preparations and measuring temperature with thermocouple and thermistor. For Figure 6(a) shows the total details from development of temperature measurement system and written by LabVIEW and the thermocouple (K-type) with the thermistor (10K ohm) were used to measure temperatures in hot water as shown in Figure 6(b) (a) Thermocouple response 838

6 (b) Thermistor response Fig. 7 The front panel response of measuring temperature with (a) thermocouple and (b) thermistor. The change temperatures both of thermocouple and thermistor are calibrated to ambient in laboratory room as shown in Figure 6. Figure 7 shows results of the experimental response in hot water with thermocouple and thermistor. It is clearly indicated that sensitivity of amplitude response more thermistor than thermocouple as the different temperatures observed. For voltage values in front panel of figure 7, which will be calculated by the interpolation method [3] and the specific formula method for using thermocouple and thermistor replaced with two types of color bars. (a) Voltage values for change temperatures (b) Change temperatures in hot water Fig. 8 Experimental response and trend lines of measuring temperature with thermocouple. (a) Voltage values for change temperatures (b) Change temperatures in hot water Fig. 9 Experimental response and trend lines of measuring temperature with thermistor. Figures 8 and 9 indicate the comparison between experimental response line and result of trend line. It is found that results exhibited of trend line very good both of linear type and power type for using thermocouple and thermistor. For thermistor response, is observed that voltage trend line decrease due to result of change voltages in 839

7 voltage divider circuit (Eq.6) as thermocouple response increase with temperatures. However, experimental response line in range times (31.29 minutes) of LabVIEW programming was completely used to data acquisition of NI USB-6009 and ADAM 4018, which can be decreased cost, easy operation, quick display and good precision. It was compared and surely found that inexpensive purchase when compare to the traditional temperature measurement device due to variable applications in engineering. Conclusions Thermocouple and thermistor are two types of instruments used for recording temperature measurements and broadly used of temperature sensing devices. Investigation of temperature was to plan on development of temperature measurement system to measure in simple change temperature, which was written by LabVIEW and developed by computer notebook connected with data acquisition (DAQ) device and then tested with a cup of hot water as put on a hot plate increased. It was clearly indicated that sensitivity of amplitude response more thermistor than thermocouple as the different temperatures observed. The experimental response line in range times (31.29 minutes) and result of trend line was found that results exhibited of trend line very good both of linear type and power type for using thermocouple and thermistor. The LabVIEW was completely used to data acquisition and decreased cost, easy operation, quick display and good precision. In addition, it was surely found that inexpensive purchase when compare to the traditional temperature measurement device due to variable applications in engineering. eferences [1] Potter, D. (1996). National Instruments. Measuring Temperature with Thermocouples-a Tutorial. Application Note 043. [2] National Instruments. (2011). Temperature Measurements with Thermocouples: How-to Guide. [3] WW, Thailand. (2009). 10 th anniversary, Product Catalog. pp [4] Calibration Procedures with thermistors. (2010). Manual ME-368. [5] Doebelin, E.. (1990). Measurement Systems Application and Design, 4 th edition, ISBN: , McGraw-Hill, Inc., Singapore. 840