Agreed I approve
Head of GCI SI Director
Deputy Director of FGU VTsSM
__________ __________
Calibration Method
temperature sensors of the KDT series.
Developed
Ch. technologist LLC "CONTEL"
Calibration Method for Temperature Sensors
KDT-50, KDT-200 and KDT-500.
1. Before starting calibration, check the compliance of the components located on the board according to the assembly drawing: KDT50.02.01SB - for KDT-50 sensors; KDT200.02.01SB - for sensors KDT-200; KDT500.02.01SB – for KDT-500 sensors.
2. Calibration of the electronic block of sensors KDT-50 and KDT-200.
2.1. Connect to the board the power supply and the equivalent of the thermometer - resistance TCM-100 according to Fig.1.
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2.3. The sequence of adjustment operations.
2.3.1.Set the voltmeter mode "U=" and the measurement limit corresponding to the value "three decimal places".
2.3.2. Set the lower value of the measured temperature on the TCM equivalent: for KDT-50 - "-500C", for KDT-200 - "00C".
2.3.3.Apply power supply.
2.3.4. Rotate the trimmer resistor RP1 to set the value of the output current 4 mA(voltmeter reading 0.400).
2.3.5. Set the upper value of the measured temperature on the TCM equivalent: for KDT-50 - "+500С", for KDT-200 - "+2000С".
2.3.6. Rotate the trimmer resistor RP2 to set the value of the output current 20 mA(voltmeter reading 20.00).
2.3.7. Repeat the operations of items 2.3.4 and 2.3.6 until the output current is established corresponding to the range
measured temperature within the error not exceeding 0,25% .
2.3.8.Check linearity at intermediate points.
2.3.9 Correspondence of measured temperature (equivalent value of resistance) and output current are given in Appendix 1.
3. Calibration of temperature sensors KDT-500.
3.1. Connect to the board the power supply and the equivalent of the thermometer - resistance Pt-100 according to Fig.2.
The polarity of the power supply connection does not matter.
-EquivalentPt100 - a special resistance box simulating a resistance thermometer of the Pt-100 type;
-V- Digital voltmeter type B7-40;
-Rn- electrical resistance coil R331;
-IP- stabilized direct current source type B5-45.
3.2 Sequence of calibration operations.
Due to the absence of adjusting elements in the product, the calibration operation is reduced to checking the operability and linearity of the conversion of resistance into current.
3.2.1. Set the voltmeter mode "U =" and the measurement limit corresponding to the value "three decimal places".
3.2.2. Set the lower value of the measured temperature on the Pt-100 equivalent: "00С".
3.2.3. Apply supply voltage.
3.2.4. Voltmeter readings must comply with 4 mA+/-0,25% (voltmeter reading 0.400).
3.3.5. Set the upper value of the measured temperature on the Pt-100 equivalent: "+5000С".
3.3.6. Voltmeter readings should correspond to 20 mA+/-0,25% (voltmeter reading 20.00).
3.3.7. Check linearity at intermediate points.
3.3.9 Correspondence of measured temperature (equivalent value of resistance) and output current are given in Appendix 2.
Note. The temperature sensor circuit KDT-500 is designed to work together with Pt-100 with W100=1.3910. The use of a resistance thermometer with W100=1.3850 leads to an increase in the basic error to 0.8% in the middle of the range.
4. After adjustment, the sensor boards are varnished. The recommended drying time is 2 days.
After drying, the boards are subject to mandatory rechecking in order to correct the output current. During this operation, it is enough to check the sensor at the ends of the range.
Executor________
Attachment 1
Correspondence of temperature, equivalent resistance and output current of KDT-50 temperature sensors.
Correspondence of temperature, equivalent resistance and output current of KDT-200 temperature sensors.
In the absence of an equivalent of TCM-100, a resistance box MCP-63 or similar should be used.
Appendix 2
Correspondence of temperature, equivalent resistance and output current of KDT-500 temperature sensors.
(for W100=1.3850)
In the absence of a Pt-100 equivalent, an MSR-63 resistance box or similar should be used.
Nbsp; LABORATORY WORK №8 Temperature measurement using resistance thermometers and bridge measuring circuits 1. The purpose of the work. 1.1. Familiarization with the principle of operation and technical device resistance thermometers. 1.2. Familiarization with the device and operation of automatic electronic bridges. 1.3. The study of two and three-wire connection of resistance thermometers.
General information.
2.1. Design and operation of resistance thermometers.
Resistance thermometers are used to measure temperature in the range from -200 to +650 0 С.
The principle of operation of metal resistance thermometers is based on the property of conductors to increase electrical resistance when heated. The heat-sensitive element of the resistance thermometer is a thin wire (copper or platinum), spirally wound on a frame and enclosed in a case.
Electrical resistance wire at a temperature of 0 0 C is strictly defined. By measuring the resistance of a resistance thermometer, you can accurately determine its temperature. The sensitivity of a resistance thermometer is determined by the temperature coefficient of resistance of the material from which the thermometer is made, i.e. the relative change in the resistance of the heat-sensitive element of the thermometer when it is heated by 100 0 C. For example, the resistance of a thermometer made of platinum wire changes by about 36 percent when the temperature changes by 1 0 C.
Resistance thermometers, for example, have a number of advantages compared to manometric ones: higher measurement accuracy; the ability to transmit readings over long distances; the possibility of centralizing control by connecting several thermometers to one measuring device (via a switch).
The disadvantage of resistance thermometers is the need for an external power source.
As secondary devices, complete with a resistance thermometer, automatic electronic bridges are usually used. For semiconductor thermal resistances, unbalanced bridges are usually used as measuring instruments.
For the manufacture of resistance thermometers, as noted above, pure metals (platinum, copper) and semiconductors are used.
Platinum most fully meets the basic requirements for a material for resistance thermometers. In an oxidizing environment, it is chemically inert even at very high temperatures, but it works much worse in a reducing environment. In a reducing environment, the sensitive element of a platinum thermometer must be sealed.
The change in the resistance of platinum within the temperature range from 0 to +650 0 С is described by the equation
R t \u003d R o (1 + at + bt 2),
where R t , R o - resistance of the thermometer, respectively, at 0 0 С and temperature t
a, b are constant coefficients, the values of which are determined when calibrating the thermometer according to the boiling points of oxygen and water.
The advantages of copper as a material for resistance thermometers include its low cost, ease of obtaining in pure form, relatively high temperature coefficient and linear dependence of resistance on temperature:
R t \u003d R o (1 + at),
where R t , R o - resistance of the thermometer material, respectively, at 0 0 С and temperature t;
a - temperature coefficient of resistance (a \u003d 4.26 * E-3 1 / deg.)
The disadvantages of copper thermometers include low specific resistance and easy oxidation at temperatures above 100 0 C. Semiconductor thermal resistance. A significant advantage of semiconductors is their large temperature coefficient of resistance. In addition, due to the low conductivity of semiconductors, it is possible to manufacture thermometers of small sizes with a large initial resistance, which makes it possible to ignore the resistance of connecting wires and other elements. electrical circuit thermometer. Distinctive feature semiconductor resistance thermometers is a negative temperature coefficient of resistance. Therefore, as the temperature rises, the resistance of semiconductors decreases.
For the manufacture of semiconductor thermal resistances, oxides of titanium, magnesium, iron, manganese, cobalt, nickel, copper, etc., or crystals of certain metals (for example, germanium) with various impurities are used. Thermal resistances of the MMT-1, MMT-4, MMT-5, KMT-1 and KMT-4 types are most often used to measure temperature. For all thermal resistances of the MMT and KMT types in the operating temperature ranges, the resistance varies with temperature according to an exponential law.
Serially available are platinum resistance thermometers (RTP) for temperatures from -200 to +180 0 C and copper resistance thermometers (TCM) for temperatures from -60 to +180 0 C. There are several standard scales within these temperature limits.
All commercially available platinum resistance thermometers have conventions: 50P, 100P, which corresponds to 0 0 С 50 ohm and 100 ohm. Copper resistance thermometers are designated 50M and 100M.
As a rule, the measurement of the resistance of resistance thermometers is carried out using bridge measuring circuits (balanced and unbalanced bridges).
2.2. Design and operation of automatic electronic balance bridges.
Automatic electronic bridges are devices that work with various sensors, in which the measured process parameter (temperature, pressure, etc.) can be converted into a change in resistance. The most widely used automatic electronic bridges are used as secondary devices when working with resistance thermometers.
circuit diagram balanced bridge is shown in Fig.1. Figure 1-a shows a diagram of a balanced bridge with a two-wire connection of the measured resistance Rt, which, together with the connecting wires, is the arm of the bridge. Arms R1 and R2 have constant resistance, and arm R3 is a rheochord (variable resistance). The power supply of the circuit is included in the ab diagonal, and the zero-device 2 is included in the cd diagonal.
Fig.1. Schematic diagram of a balanced bridge.
a) two-wire connection scheme
b) three-wire connection scheme.
The scale of the bridge is located along the reochord, the resistance of which, when Rt changes, is changed by moving the slider 1 until the zero pointer of the device 2 is set to zero mark. At this moment, there is no current in the measuring diagonal. Slider 1 is connected to the scale pointer.
When the bridge is in equilibrium, the equality
R1*R3=R2*(Rt+2*Rpr)
Rt=(R1/R2)*R3-2*Rpr
The resistance ratio R1 / R2, as well as the resistance of the connecting wires Rpr for this bridge, are constant values. Therefore, each value of Rt corresponds to a certain resistance of the reochord R3, the scale of which is graduated either in Ohms or in units of a non-electric quantity, for which the circuit is intended to measure, for example, in degrees Celsius.
In the presence of long wires connecting the sensor to the bridge in a two-wire circuit, the change in resistance and depending on temperature environment(air) can introduce significant errors in the measurement of resistance Rt. A radical means of eliminating this error is to replace the two-wire circuit with a three-wire one (Fig. 1-b).
In a balanced bridge circuit, changing the power supply voltage does not affect the measurement results.
In automatic balanced electronic bridges, the following circuit is used to balance the circuit. A schematic diagram of an electronic bridge type KSM is shown in Fig.2. The operation of the electronic bridge is based on the principle of measuring resistance using the balanced bridge method.
The bridge circuit consists of three arms with resistances R1, R2, R3, a reochord R and a fourth arm containing the measured resistance Rt. A power supply is connected to points c and d.
When determining the resistance value, the currents flowing through the shoulders of the bridge create a voltage at points a and b, which is fixed by a zero indicator 1 connected to these points. By moving the slider 2 of the rheochord R with the help of a reversible motor 4, one can find such an equilibrium position of the circuit at which the voltages at points a and b will be equal. Therefore, by the position of the slider 2 of the reochord, one can find the value of the measured resistance Rt.
At the moment of equilibrium of the measured circuit, the position of arrow 3 determines the value of the measured temperature (resistance Rt). Registration of the measured temperature is given with pen-5 in diagram 6.
Electronic bridges are divided according to the number of measurement points and records into single-point and multi-point (3-,6-,12- and 24-point), with a tape diagram and devices with a disk diagram. Electronic bridges are available in accuracy classes 0.5 and 0.25.
The recording device of a multipoint device consists of a printing drum with dots and numbers printed on its surface.
Devices are powered by the mains alternating current voltage of 127 and 220V, and the measuring circuit of the bridge is powered by a direct current of 6.3 V from a power transformer device. Dry-cell powered devices are used in cases where the sensor is installed in fire hazardous areas.
Calibration of temperature sensors
The resistance temperature converter is connected to the measuring device using copper (sometimes aluminum) wires, the cross section, length, and, consequently, the resistance of which is determined by the specific measurement conditions.
Depending on the method of connecting the resistance thermal converter to the measuring device - according to a two-wire or three-wire circuit (Fig. 1, option "a" and "b"), the resistance of the wires enters entirely into one arm of the instrument's bridge circuit, or is divided equally between its arms. In both cases, the readings of the device are determined not only by the resistance of the resistance thermocouple, but also by the connecting wires. The degree of influence of the connecting wires on the readings of the device depends on the value of their resistance. So, in each specific measurement conditions, i.e. for each specific value of this resistance, the readings of the same device measuring the same temperature (when the thermal converter has the same resistance) will be different. To eliminate such uncertainty, measuring instruments are calibrated at a certain standard resistance of the connecting wires, which is necessarily indicated on their scale by a record, for example, R ext \u003d 5 Ohm. If during operation of the device the connecting line will have the same resistance, the readings of the device will be correct. Therefore, measurements should be preceded by the operation of fitting the connecting line, which consists in bringing its resistance to the specified calibration value R ext.
The resistance of the connecting line, even with careful adjustment, is equal to the calibration value only if the ambient temperature does not differ from that at which the adjustment was carried out. A change in line temperature will lead to a change in the resistance of copper (aluminum) wires, a violation of the correct fit and, ultimately, to the appearance of a temperature error in the instrument readings. This error is especially pronounced for a 2-wire communication line, when the temperature increment of the line resistance takes place in only one arm of the bridge circuit. With a 3-wire line, the temperature increment of the line resistance is received by two adjacent arms and the state of the bridge circuit changes less than in the first case. As a result, the temperature error is smaller. Therefore, 3 wire line turns out to be more preferable, despite the greater consumption of material used for the manufacture of connecting wires.
The order of the work.
4.1. Familiarize yourself with the principle of operation and design of resistance thermometers and electrical devices of the stand. Assemble a two-wire measurement circuit in accordance with fig. 3a.
4.2. Set the toggle switch to the 2-wire position and the switch to the 0 position.
4.3. Set the MC bridge, simulating a resistance thermometer, to the resistance in Ohms corresponding to the tabular data (Table 1), take temperature readings in 0 C on the MPR51 scale and calculate the absolute and relative measurement errors indicated in Table 1 of temperatures.
Investigation of 2-wire circuit.
4.4. Set the toggle switch to 2-wire connection.
4.5. Set the resistance switch of the connecting wires to position 1 (corresponds to R pr \u003d 1.72 Ohm).
4.6. Follow paragraph 4.3 and enter the measurement results in table 1 in lines 5-7, corresponding to a 2-wire connection at R pr \u003d 1.72 Ohm.
4.7. Set the resistance switch of the connecting wires to position 2 (corresponds to R pr \u003d 5 Ohm).
4.8. Follow paragraph 4.3 and enter the measurement results in table 1 in lines 8-10 corresponding to a 2-wire connection at R pr \u003d 5 Ohm.
Study of 3-wire circuit.
4.9. Set the toggle switch to the position of the 3-wire connection diagram (Fig. 3 b).
4.10. Complete steps 4.5-4.8 and enter the results in lines 11-16 of Table 1 corresponding to the resistances of the connecting wires R pr \u003d 1.72 Ohm and R pr \u003d 5 Ohm.
4.11. To give an analysis of the accuracy of measurements with a two-wire and three-wire measurement scheme.
4.12. In the report, provide conclusions on the test protocol (Table 1).
Test questions.
1. Name the types of resistance thermometers and their principle of operation.
2. Name the advantages and disadvantages of resistance thermometers.
3. Give examples of the use of resistance thermometers in automatic control and regulation systems.
4. What is the purpose of automatic electronic balance bridges?
5. The principle of operation of balanced bridges.
For certain control purposes, such as control of a heating plant, it may be important to measure the temperature difference. This measurement can be carried out, in particular, by the difference between the outside and inside temperatures or the inlet and outlet temperatures.
Rice. 7.37. Measuring bridge for determining the absolute values of temperature and temperature difference at 2 points; U Br is the bridge voltage.
The principal device of the measuring circuit is shown in fig. 7.37. The scheme consists of two Wheatstone bridges, and the middle branch (R3 - R4) of both bridges is used. The voltage between points 1 and 2 indicates the temperature difference between Sensors 1 and 2, while the voltage between points 2 and 3 corresponds to the temperature of Sensor 2, and between points 3 and 1 the temperature of Sensor 1.
Simultaneous measurement of temperature T 1 or T 2 and temperature difference T 1 - T 2 is important in determining the thermal efficiency of a heat engine (Carnot process). As you know, the efficiency W is obtained from the equation W \u003d (T 1 - T 2) / T 1 \u003d ∆T) / T 1.
Thus, to determine, you only need to find the ratio of the two voltages ∆U D 2 and ∆U D 1 between points 1 and 2 and between points 2 and 3.
Precise adjustment of the described temperature measuring instruments requires rather expensive calibration devices. For the temperature range 0...100°C, quite accessible reference temperatures are available to the user, since 0°C or 100°C, by definition, are respectively the points of crystallization or boiling point of pure water.
Calibration at 0°C (273.15°K) is carried out in water with melting ice. To do this, an insulated vessel (for example, a thermos) is filled with heavily crushed pieces of ice and filled with water. After a few minutes, the temperature in this bath reaches exactly 0°C. By immersing the temperature sensor in this bath, the sensor readings corresponding to 0°C are obtained.
The same applies for calibration at 100°C (373.15 K). A metal vessel (for example, a saucepan) is half filled with water. The vessel, of course, should not have any deposits (scale) on the inner walls. By heating the vessel on the stove, bring the water to a boil and thereby reach the 100-degree mark, which serves as the second calibration point for the electronic thermometer.
To check the linearity of a sensor calibrated in this way, at least one more control point is required, which should be located as close as possible to the middle of the measured range (about 50 ° C).
To do this, the heated water is again cooled to the specified area and its temperature is accurately determined using a calibrated mercury thermometer with an accuracy of 0.1°C. In the temperature range of about 40 ° C, it is convenient to use a medical thermometer for this purpose. By accurately measuring the water temperature and the output voltage, a third reference point is obtained, which can be considered as a measure of the linearity of the sensor.
Two different sensors, calibrated by the method described above, give identical readings at points P 1 and P 2, despite their different characteristics (Fig. 7.38). An additional measurement, such as body temperature, reveals the non-linearity of the characteristic IN sensor 2 at point P 1 . Linear characteristic BUT sensor 1 at point P 3 corresponds exactly to 36.5% of the total voltage in the measured range, while the non-linear characteristic B corresponds to a clearly lower voltage.
Rice. 7.38. Determination of the linearity of the characteristics of the sensor with a range of 0...100ºС. Linear ( BUT) and nonlinear ( IN) the characteristics of the sensors coincide at the reference points of 0 and 100ºС.
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Temperature sensors made of platinum and nickel
Thermocouples
Silicon temperature sensors
Integrated temperature sensors
temperature controller
NTC thermistors
PTC thermistors
PTC thermistor level sensor
Temperature difference measurement and sensor calibration
PRESSURE, FLOW AND SPEED SENSORS
Like temperature sensors, pressure sensors are among the most widely used in technology. However, for non-professionals, pressure measurement is of less interest, since existing pressure sensors are relatively expensive and have only limited use. Despite this, consider some options for their use.
The calibrator can be used as both a dry-well and a liquid thermostat. The calibrator uses a unique gas-fired Stirling heat pump (FPSC) technology to cool the thermostat down to -100°C. Appearance workplace is shown in Figure 4.
Figure 4 - Appearance of the workplace
The calibrator thermostat has two zones with separate regulation. The regulator of the lower zone maintains the set temperature value, and the upper zone maintains a "zero" temperature difference relative to the lower zone. This method ensures high temperature uniformity in working area and low error of its task.
The Calibrator is equipped with an external reference RTD signal measurement circuit. Such a thermometer is installed next to the verified sensor and connected to a special connector of the calibrator. This greatly simplifies the calibration by the comparison method, which has a much smaller error.
The calibrator is equipped with a DLC circuit - dynamic compensation for the effect of heat loss through the sensors under test. The DLC thermometer is installed next to the probe to be verified, it measures the temperature difference in the working area of the insert tube and controls the regulator of the thermostat's upper zone. This ensures high uniformity of temperature distribution in the working area up to 60 mm from the bottom of the tube, regardless of the number and/or diameter of the inserted sensors.
The calibrator allows you to measure the signals of verified thermocouples and resistance thermometers (mV, Ohm, V, mA) in accordance with GOST, IEC and DIN.
Unique Features:
Lowest border negative temperature-100°C;
Extremely high stability;
High temperature uniformity in the working area up to 60 mm from the bottom of the insert tube;
Low error;
Unparalleled dynamic compensation circuit for the effect of thermostat loading;
Rapid heating, cooling;
Full compensation of the influence of surges and instability of the mains supply;
Built-in means for measuring the output signals of various temperature sensors;
Built-in circuit for measuring the signal of an external reference intelligent resistance thermometer, in whose memory individual calibration coefficients are stored;
Saving calibration/verification results during internal memory calibrator;
Friendly Russified menu-based user interface;
Full automation of verification/calibration of temperature sensors both in stand-alone mode and when working with a PC running software, including verification of several sensors simultaneously using ASM-R switches.
In addition to providing temperature settings, the calibrator automatically performs verification/calibration in a stepwise temperature change mode, as well as (in version B) thermal relay calibration.
Russified software allows:
Verify temperature sensors in automatic mode or upload verification/calibration tasks to the calibrator and, after completing it in offline mode, transfer verification results to a PC.
Recalibrate the calibrator for temperature and electrical signals.
The software provides access to the management of all functions of the calibrators and, in addition, allows you to load multiple calibration tasks into the calibrator and, after their execution, in stand-alone or automatic modes, transfer the results to a personal computer for processing and storage.
Using the software, you can adjust the internal ("READ") thermometer of the calibrators, as well as the channels for measuring electrical quantities, including the channel of the external ("TRUE") thermometer. Given software allows loading into the calibrator a calibration characteristic for an external resistance thermal converter of increased accuracy.
Software structure:
Support for calibrated/calibrated temperature measuring instruments;
Configuration of the scheme for verification/calibration of temperature measuring instruments;
Temperature MI check/calibration scheduler;
Verification/calibration of temperature measuring instruments using a PC.
Connectors for connecting to a computer, as well as for connecting external devices are shown in Figure 5.
Figure 5 - Digital connectors.
Application #4: Temperature sensor calibration.
Upon release from production, the temperature sensor built into the amperometric sensor is calibrated according to the procedure, the execution algorithm of which is recorded in the service menu of the analyzer. You should only calibrate the temperature sensor when replacing the sensor with a new one. In this case, connect the new sensor to measuring device and turn on the analyzer. To calibrate the temperature sensor, you need to assemble the installation shown in the figure. This setting should provide three temperature scales in the range of 5-50°C. in a simple way. To do this, you need a thermos, a glass of distilled water at room temperature and a plastic glass with ice. Pour distilled water heated to 50 +5 ° C into a thermos. Make a hole with a diameter of 10 mm in a glass with ice. To increase the diameter of this hole to 16 mm, fill it with warm water. After 5-10 minutes, the water in the hole will have an ice melting temperature of ~ 0 o C.
To calibrate the temperature sensor, go to the service calibration menu. To do this, enter the Calibration menu and, while holding the "DOWN" key, press the "ENTER" key. In the service menu that appears, select the "TEMPERATURES" option, press "ENTER". 
In the window that opens, select the "Low point" option and press "ENTER".
Immerse the sensor and the reference thermometer in a temperature-controlled beaker with a temperature of the bottom mark of the scale: 5 + 1 o C or in a well in a beaker with ice. 
In the window that opens, enter the temperature of the low point using the cursor keys and press "ENTER".
After a successful low point calibration message, the temperature sensor calibration menu will reappear on the screen. Select the Top Point option and press ENTER.
Immerse the sensor and the reference thermometer into a temperature-controlled beaker or thermos with the temperature of the top mark of the scale and, after waiting for the thermometer readings to settle, press "ENTER". 
Read the reference thermometer reading and use the cursor keys to enter this value.
If the high point calibration is successful, the temperature sensor calibration menu will reappear on the screen. Select the "T Correction" option and press "ENTER".
Follow the instructions shown on the analyzer display and press ENTER.
Wait until the thermometer readings are established and press "ENTER". 
Read the temperature reading from the reference thermometer and enter this value using the keypad. Press "ENTER".
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