Study of Characteristics of Temperature Sensor Using Thermocouple and RTD Sensor

Experiment 1: STUDY OF CHARACTERISTICS OF TEMPERATURE SENSOR USING THERMOCOUPLE AND RTD SENSOR

Abstract:

In this experiment, the main focus was on the measurement of the temperature with the help of the various method, these methods are used to relate with each methods and to determine the variance among the data collected from each method. Method used in this experiment consist of thermistor, thermocouple, and a platinum resistance thermometer (RTD), self heating infrared and lab view. Each method showing reading for the water temperature in ohms/ volt. To collect the readings of the used methods, eight various temperature of water are used to check the temperature of water it is very closed to the desired temperature value. To confirm the accuracy of the method used the result of the data is show through the graphs of the calculated data for the each method.

 

Introduction

In this experiment, while using thermocouple and RTD sensor we will study the characteristics of a temperature sensor. It is very difficult objectives to calculate accurate reading by a sensor for industrial instrumentation. Accurate measurement plays a major role in industries. So, for this experiment, we are using different apparatus in this experiment like:

• Transducer trainer kit
• Thermocouple
• Heater
• RTD( PT100 )
• Thermometer
• Multi meter
• Beaker
• Connecting probes
• Stopwatch

 

 

Objective:

1. To understand the sensors concept and measurement.

2. To measure and to study the characteristics of Thermocouple and RTD sensor.

Overview:

Thermocouple

Accurate temperature is most important parameter used in the modern industrial instruments, but achieving accurate temperature is very complicated and difficult, so to reduce the difficulties proper temperature sensors are to be used either deal with the inaccuracies in temperature reading. So to obtain very accurate result there is a instrument used is thermocouple in modern industries because of its inherent, accuracy, wide temperature range suitability, rapid thermal response, highly reliable, cheaper in cost, varied range of applications.(1)Johann See-beck.

Uses of thermocouple is varied and very much in use at places like meat probes for direct temperature storage, temperature affected control system, ovens controlled by thermocouple, also controls the energy in various forms going to the control system.

RTD Sensor

 

RTD stands for Resistance Temperature Detector it is the most accurate sensor. In this the resistance is proportional to the temperature. This sensor is made from the platinum, nickel and copper metals. It can be used to measure the temperature up to +850. It required an external current source to work properly. The current produces heat in a resistive element causing an error in temperature measurement. This error is calculated by this formula:

$\mathit{delta\; T}=p*s$

 

Achievements to be done by performing this experiment:

Thermocouple:

• Characteristics of thermocouple.

• Application of thermocouple
• Thermo electrical laws

RTD sensor

• Characteristics of RTD sensor.

• Application of RTD sensor.
• Working principle of RTD sensor.

A block diagram shows how we calculated the temperature and voltage by using an thermocouple and RTD sensor:

Instrumentation amplifier

Thermocouple

Gain Amplifier

MULTIMETER

 

 

 

RTD

Instrumentation amplifier

Gain Amplifier

MULTIMETER

 

 

Fig.1. block diagram of procedure to calculate the temperature and voltage using thermocouple and RTD sensor

 

 

 

 

 

Working principle

When we are talking about the working principle of thermocouple and RTD sensor to measure the temperature in this experiment we use the transducer trainer kit. Including banana socket for thermocouple as shown by the yellow circle in FIG 2.

              

Fig.2 showing the Banana socket in yellow circle

First, we have done this experiment for only thermocouple readings.

Now, we are connecting the output of the thermocouple yellow pin (T 14) to the corresponding blue terminal (T 15). Now we connect the output of thermocouple circuit (T 16) to (V+) of digital panel meter and the (GND) ground terminal of digital panel meter to (V-) terminal  as shown  in fig. 3

              

Fig.3. showing transducer trainer kit electrical circuit

Than we turn on the switch sw1 and sw4 of the digital panel meter. After that, we turn on the instrument for 2-3 minutes to get it warm to get the better result.

Afterward that we apply the heat to water and measure the temperature by thermocouple sensor then we can see there is a corresponding change in the digital panel meter. When the temperature is increased in thermocouple sensor we can see that the digital panel meter reading increases slowly respectively.

 

Finally, we note the thermocouple reading from 60°C upto 94°Cat different temperatures.

Than  we have done this experiment for RTD sensor:

For that firstly we put the RTD sensor input (blue) at the terminal T17 in the transducer trainer board. Then, we connect the other output pins of the RTD sensor into the T18 and T19 port of the trainer.

Than, we turn on the switch SW2 and turn on the power or leave the module again for 2-3 minutes.

At the next step is to apply the thermocouple after heating after heating, we leave the water at high temperature(93°C) in the beaker to cool down.

when the water temperature decrease, then we note the temperature reading at a regular interval of time by dipping thermocouple sensor in water and the digital panel meter reading also will decrease accordingly to the temperature.

 we calculate the voltage with the help of the RTD sensor at different temperature readings.

 

Procedure to perform the experiment

Thermocouple

• Insert the thermocouple to the banana socket than  connect the output of the thermocouple pins (yellow and green) to the trainer pins (yellow and green) respectively.
• Connect Op amplifier output to positive end of digital panel meter and ground to negative end of digital panel meter.
• Connect switch 4 to B and push toggle switch towards downward.
• Switch 1 should be ON.
• Switch ON the instrument and leave it for 3-4 mins to warm up and obtain accurate result.
• Note the reading in digital panel meter because it will indicate room temperature.
• After that let the sensor come in contact with the heat and note the change in digital panel meter because there will be change in temperature reading as well as voltage also.
• Than notice the thermocouple readings at different temperature, and indicates the slow change in increase in voltage and also the temperature will rise.
• Plot the graph of temperature Vs voltage.

RTD Sensor.

• Insert input pin of RTD Sensor to T17 of trainer.
• Connect sensor outputs (yellow and black pins) to sensor input at T18 and T19 (Yellow and black) respectively on trainer.
• Connect output amplifier T20 to positive end of the digital panel meter and ground to negative end of the digital panel meter.
• Push switch 4 towards B and toggle switch towards downwards.
• Functioning will be obtained by ensuring the switch 2 is ON.
• Switch ON the power supply.
• After warming up the system let the sensor come in contact with heat to notice the change in digital panel meter.
• Decrease in temperature will result in decrease in voltage and vice a versa.

 

Observation sheet:

At the very first we calculated the readings of the temperature and voltage of the thermocouple sensor with the help of instruments and the collected data

Thermocouple

No.	Temperature (°C)	Voltage (V)
1	93	8.6
2	92	8.3
3	91	8.2
4	90	8.1
5	89	8.0
6	88	7.9
7	87	7.8
8	85.5	7.6

 

Table 1: cool down temperature reading of the thermocouple sensor

• At the second step we observed the voltage of the RTD sensor at the random intervals of time Where we got the eight different readings for the same RTD sensor as shown in the         below table:

 

 

 

 RTD sensor

No.	Time ( sec )	EMF ( MV )
1	0	93
2	30	92
3	60	91
4	90	90
5	110	89
6	142	88
7	180	87
8	240	85.5

 

Table 2: The voltage readings of RTD sensor at different time sequence

 

• Next to it, we have calculated the RTD sensor heating temperature and voltage within a cooling temperature of thermocouple sensor readings and the observed data are given in table 3

 

	EMF ( MV )
Temperature	Heating	Cooling temperature
65	5.6	93
69	6.8	93
77	7.5	91
81	7.7	90
84	8.1	89
86	8.2	88
89	8.4	87
93.5	8.5	85.5

 

Table 3: for the different readings of the heating temperature, cooling temperature and voltage of the RTD sensor

Description and analysis: Thermocouple:

It was originally discovered by T.J. SEEBECK in 1821, also he gave the concept that there is a flow of current when the two ends of conductor are at different temperature that means that there is proportionality between voltage and temperature differences. His discovery of thermocouple is nowadays cost effective thermocouple temperature sensors.

Thermocouple is a device used to measurement temperature is built up by two dissimilar metals which in return generates a very small portion of electric potential with a very small range of voltage in mV, these two ends of metals goes into a tube which is closed at one end and other ends are connected to the circuit for detecting temperature difference and or control system.

Two ends of metals are joined by welding so selecting metals depends on the wide range of temperature to be measured. Voltage being so small we require electronic device to make that small value of voltage useful or it mostly connected to a electrical circuit which in return directly shows the temperature.

Laws of thermo electric:

• 
  The first law states that the circuit of a single homogeneous metal cannot sustain the electric current therefore varying in parts, by providing heat alone, deflection in current heats up the wire and is used as evidence of homogeneous wire.

Figure 2. block diagram of thermocouple

 

• The law of successive or temperature states that if two dissimilar metals produce thermal EMF of E1 at temperature T1 and T2 and thermal EMF of E2 at temperature T2 and T3 than the E1+E2 will be found value at temperature T1 and T2.

RTD sensor:

There are 3 styles of RTDs that are as follows:

 

Figure 3: block diagram of RTD sensor

There are 3 styles of RTDs that are as follows:

• RTD Elements.

It is the simplest form of RTD, and it consists of wire coiled around a piece of glass or ceramic core. Due to its very small size it is used in a places of limited area of placement.

• RTD Surface Elements.

It is designed very thin as possible to gather good connection of flat surface temperature measurement and it makes it very special type of RTD sensor.

• RTD Probes

RTD element is fitted inside the metal core tube called sheath to protect it from environment, it is called the most rugged form of RTD

Resistance thermometers

It offers greater stability, accuracy because thermocouple uses See-beck effect to generate voltage and resistance thermometer uses electrical resistance and requires very less power to get functioning condition. There is a linear relation between resistance and temperature and platinum is the best material to use in resistance thermometers due to its linear relation of temperature and resistance and chemical alertness.

 Platinum resistance thermometers (PRTs)

 

Temperature range it provides with a great accuracy is between (-200°C to 850°C). These is used to measure the resistance of platinum element. If a small amount of current is passed through it than it measure very accurate resistance, due to its very fragile nature it should be taken care of to avoid resistive heating, strains on resistance.

RTD’s industrial application is rarely above 660°C because due to contamination property of platinum at high temperature by reaction with metals.

 

 

Conclusion

By combining 3 basic laws of thermo electric, it can be concluded that electric current cannot be sustained by a single homogeneous metal, than any one of the junction from all is maintained at some specific temperature to take it as a initial reference point therefore the EMF generated at that point depends only on the temperature on that specific junction and can be taken as the measurement of its temperature.

EXPERIMENT 2: STUDY OF CHARACTERISTICS OF STRAIN GAUGE BASED LOAD CELL

 

Abstract

 

We are performing this experiment to study the characteristics of the load cellsensors  based on the strain gauge . while performing this experiment we study that how the strain gauge load cells are working and how they expressing the voltage and load.

Strain gauges are resistive sensors joined at the critical location on the surface of structural components to detect surface deformation and, thus, to measure the mechanical stress. Load cell sensor is the major example of it which uses electrical strain gauges. The unknown load is measured by sensing the strain developed in the electrical member while using the load cell. The load is linearly related to strain as long as the mechanical member remains elastic. The load cells can be easily calibrated so that the output signal is proportional to the load. The thermal coefficient of material can be determined by the gauges.

Introduction

Strain gauges are sensors which are used in variety of physical measurements. They change resistance when they are stretched or compressed. Because of this property, strain gauges often are bonded to a solid surface and used for measuring acceleration, pressure, tension and force. We can use the measurement of tension to determine the weight applied to the load cell. Fundamentally, strain is a change in length per unit length. For instance, if a 1 m long beam is stretched to 1.000002 m, the strain is 2 micro strains. One characteristic of strain gauges are gauge factor, and is defined as fractional change in resistance divided by the strain. There are number of load cells based on strain gauge:

• Pneumatic load cell
• S type load cell
• Pancake load cell
• Bending beam load cell
• Strain gauge load cell

OBJECTIVE

We are performing this experiment

1. To understand and study the load cell trainer fundamental and concept.

2. To measure the characteristic of Voltage and Load.

Working principal

Essentially, the pressure load cell is a module intended to hold the heap at the pressure estimation point. The ductile dynamometer estimates pressure, and the compressive dynamometer estimates push along one pivot. For the most part, the pressure load cell is situated under the item to be estimated.

In our experiment we are using the load cell sensor trainer kit which is shown in the below figure:

Figure.1. strain gauge based load cell

 

As a first step we connect the load cell sensor trainer kit and also connect its circuit with the help of wires. we connected the black and red pins of load sensors into T11 and T12 respectively.

Than we provided the voltage supply to the load cell by connecting the green and blue pins to the T9 and T10 sockets respectively. In the next step we connected the load cell trainer kit output into the v+ and GND in v- in digital panel meter.

Than we applied the load to the load cell sensor and we noted the corresponding change in to voltage in the digital multimetre. As we increasing the load to load cell the reading of the digital multimeter was also changed.

Theory background

Load sensor: load cells stand out as one of the most important transducers. Basically, these transducers measure deformations produced by force or weight. In addition, according to the type of output signal they generate and the way they detect the weight, there are many types of load cells, for instance: strain gauge cells, mechanical cells, and other types (fibre optic, piezo resistive, and so on). However, due to their high accuracy and low cost, strain gauge load cells are the most used in today’s industry. Most of today’s load cell designs use strain gauges as the sensing element. strain gauge based load cell are working on the basis of the Wheatstone bridge principle as shown in fig.2

Figure.2 Wheatstone bridge principle

Basic information about some types of load cells

Pneumatic load cell: In the pneumatic type of load cell air pressure is used tomeasure the weight of the object. When the air pressure is applied to system air passes through one end of the system to an nozzle connected at the bottom of the load cell.

Piezoelectric load cell: They work a similar route as pressure check load cells, however there is constantly a major contrast between the voltage readings of the two burden cells.

Vibrating load cell: Vibrating line load cells (helpful in geo mechanical applications because of little float), and capacitive burden cells in which the capacitance of the capacitor changes as the heap presses the two plates of the capacitor together.

Requirement of this experiment

For this experiment we need some electronic hardware components. These are the main part of this experiment and play major role during the experiment. There is a list of apparatus which we need for this experiment.

• transducer trainer kit

• weights
• load cell assembly
• multimeter
• connecting probes

All the apparatus are shown in the below figure in working setup:

      

Block diagram

The block diagram draw below is helping to understand the working of the strain gauge based load cell and this also help to understand the accurate voltage output structure. figure4:

Instrumentation

amplifier

      Load cell

Wheatstone  bridge

     multimeter

Gain amplifier

Observation sheet

During this experiment we observed the different output voltage reading with a particular change to the load in this experiment.

When we applied the different conditions on this experiment like first I will see the output voltage in unload condition and then in the applied load condition. After that, we increased the weight in a particular sequence and observed the different output voltage changes as shown in the table:1

 

Table: 1

	Applied load( Kg)		Output voltage(mv)		%Error
No.	Load	Unload	Load	Unload	Load	Unload
1	0gm	0	93	93	0	0
2	400gm	0	135	93	0	0
3	800gm	0	183	93	0	0
4	1200gm	0	217.5	93	0	0
5	1600gm	0	265	93	0	0
6	2000gm	0	300	93	0	0

As shown in table 1, we observed that when I applied 400 gm weight than the load cell sensor deforms and gives the output voltage is 135 mv. After that, we have increased the weight and reaches up to 2 kg and the output voltage on 2kg weight is 300 mv.

 

Conclusions

In conclusion, we compared the different types of strain gauges and examining the difference between the strain gauges:

There are three different types of strain gauges:

• tubular strain gauges
• mesh strain gauge
• foil strain gauges

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