CN217358783U - Two-wire system thermocouple temperature transmitter with cold end temperature compensation - Google Patents
Two-wire system thermocouple temperature transmitter with cold end temperature compensation Download PDFInfo
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- CN217358783U CN217358783U CN202220874064.4U CN202220874064U CN217358783U CN 217358783 U CN217358783 U CN 217358783U CN 202220874064 U CN202220874064 U CN 202220874064U CN 217358783 U CN217358783 U CN 217358783U
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Abstract
The utility model discloses a two-wire thermocouple temperature transmitter with cold end temperature compensation, which comprises a cold end temperature compensation circuit and an XTR101AP conversion circuit; the A end of the thermocouple is connected with the XTR101AP conversion circuit, the B end of the thermocouple is connected with the cold end temperature compensation circuit and the XTR101AP conversion circuit, and the XTR101AP conversion circuit is also connected with the cold end temperature compensation circuit. The utility model discloses a 4 ~ 20mA two-wire system special chip XTR101AP of high accuracy low drift to innovatively add high accuracy current type temperature sensor AD590 and carry out the design of thermocouple cold junction precision compensation circuit, form the two-wire system thermocouple temperature transmitter of the high accuracy precision cold junction compensation of unique excellent performance.
Description
Technical Field
The utility model relates to a take two-wire system thermocouple temperature transmitter of cold junction temperature compensation belongs to the temperature detection field.
Background
The thermocouple is a widely used temperature sensor, which generates thermoelectric force due to temperature difference between a hot end (in a measured temperature field) and a cold end (in an external environment), and the thermoelectric force can be amplified and converted by a temperature transmitter to output a 4-20mA current signal, thereby facilitating transmission and measurement. In order to make the output of the temperature transmitter only related to the measured temperature, cold end temperature compensation measures need to be taken. XTR101AP is a 4 ~ 20mA two-wire system transmitter special chip of high accuracy low drift that commonly uses, and the conventional application scheme is to use the diode to realize cold junction temperature compensation in XTR101 AP's peripheral circuit, but because the temperature characteristic (the relation of drop and temperature) of diode is the nonlinear relation, therefore, the precision is not high when the diode is used as cold junction temperature compensation, leads to the temperature transmitter measuring error great. Therefore, it is desirable to provide a temperature transmitter capable of achieving high-precision cold end temperature compensation.
Disclosure of Invention
The utility model provides a take two-wire system thermocouple temperature transmitter of cold junction temperature compensation utilizes high accuracy current type temperature sensor AD590 to carry out thermocouple cold junction compensation circuit design through XTR101AP chip and cooperation, has formed the two-wire system thermocouple temperature transmitter who takes accurate cold junction temperature compensation.
The technical scheme of the utility model is that: a two-wire system thermocouple temperature transmitter with cold end temperature compensation comprises a cold end temperature compensation circuit and an XTR101AP conversion circuit; the A end of the thermocouple is connected with the XTR101AP conversion circuit, the B end of the thermocouple is connected with the cold end temperature compensation circuit and the XTR101AP conversion circuit, and the XTR101AP conversion circuit is also connected with the cold end temperature compensation circuit.
Further comprising: the current expanding circuit is connected with the XTR101AP conversion circuit and the reverse connection preventing circuit, and the reverse connection preventing circuit is further connected with the XTR101AP conversion circuit.
The cold end temperature compensation circuit comprises a resistor R1, a resistor R2, a resistor R3 and a temperature sensor AD 590; the connection line of one end of the resistor R3 and the end B of the thermocouple is connected with the 10 pin of the XTR101AP in the XTR101AP conversion circuit, the connection line of the other end of the resistor R3 and one end of the resistor R2 is connected with the cathode of the temperature sensor AD590 and one end of the resistor R4 in the XTR101AP conversion circuit, the connection line of the anode of the temperature sensor AD590 and one end of the resistor R1 is connected with the 11 pin of the XTR101AP in the XTR101AP conversion circuit, and the connection line of the other end of the resistor R1 and the other end of the resistor R2 is connected with the 3 pin of the XTR101AP in the XTR101AP conversion circuit.
The XTR101AP conversion circuit comprises an XTR101AP, a resistor Rs, a resistor R4, a capacitor C1 and a capacitor C2; the 3 feet of the XTR101AP are connected to a connecting line of a resistor R1 in the cold-end temperature compensation circuit and a resistor R2 in the cold-end temperature compensation circuit, one end of a capacitor C1 is grounded, the other end of the capacitor C1 is connected to a connecting line of a 4 foot of the XTR101AP and the A end of the thermocouple, two ends of a resistor Rs are respectively connected with a 5 foot and a 6 foot of the XTR101AP, one end of the resistor R4 is connected to a connecting line of a resistor R3 and a resistor R2 in the cold-end temperature compensation circuit, a 7 foot of the XTR101AP is connected with the other end of a resistor R4, the capacitor C2 is connected in parallel to two ends of the resistor R4, a 10 foot of the XTR101AP is connected to a connecting line of a resistor R3 and the B end of the cold-end temperature compensation circuit, and an 11 foot of the XTR101AP is connected to a connecting line of a positive electrode and a resistor R1 of a temperature sensor AD590 in the cold-end temperature compensation circuit.
The current expanding circuit comprises a triode Q1 and a resistor R6; one end of the resistor R6 is connected to a connection line of an 8 pin of the XTR101AP in the XTR101AP conversion circuit and a cathode of the diode D1 in the anti-reverse connection circuit, the other end of the resistor R6 is connected with a collector of the triode Q1, a base of the triode Q1 is connected with a 12 pin of the XTR101AP in the XTR101AP conversion circuit, and an emitter of the triode Q1 is connected with a 9 pin of the XTR101AP in the XTR101AP conversion circuit.
The reverse connection preventing circuit comprises a diode D1, a capacitor C3, an output end positive end and an output end negative end; the connection line of the cathode of the diode D1 and the 8 pin of the XTR101AP in the XTR101AP conversion circuit is connected with a resistor R6 in the current-expanding circuit, the connection line of the anode of the diode D1 and the positive end of the output end is connected with one end of a capacitor C3, the other end of the capacitor C3 is connected with the connection line of the 7 pin of the XTR101AP in the XTR101AP conversion circuit and the negative end of the output end, and the positive end of the output end and the negative end of the output end are connected with an external circuit.
The utility model has the advantages that: the utility model discloses a 4 ~ 20mA two-wire system special chip XTR101AP of high accuracy low drift to innovatively add high accuracy current type temperature sensor AD590 and carry out the design of thermocouple cold junction precision compensation circuit, form the two-wire system thermocouple temperature transmitter of the high accuracy precision cold junction compensation of unique excellent performance.
Drawings
FIG. 1 is a schematic circuit diagram of the present invention;
fig. 2 is a schematic diagram of the "cold junction temperature compensation circuit + TR101AP switching circuit" and its equivalent circuit.
Detailed Description
Example 1: as shown in fig. 1-2, a two-wire thermocouple temperature transmitter with cold end temperature compensation comprises a cold end temperature compensation circuit, an XTR101AP conversion circuit; the A end of the thermocouple is connected with the XTR101AP conversion circuit, the B end of the thermocouple is connected with the cold end temperature compensation circuit and the XTR101AP conversion circuit, and the XTR101AP conversion circuit is also connected with the cold end temperature compensation circuit.
Further, it may be provided that the method further includes: the current expanding circuit is connected with the XTR101AP conversion circuit and the reverse connection preventing circuit, and the reverse connection preventing circuit is also connected with the XTR101AP conversion circuit and an external circuit. Specifically, the cold end temperature compensation circuit realizes cold end temperature compensation of the thermocouple; XTR101AP conversion circuit for realizing input voltage e IN Is converted into an output current I O (ii) a The current-spreading circuit is used for shunting partial current of an internal transistor of the XTR101AP to reduce power consumption, internal heat generation and temperature influence of the XTR101AP, so that the precision and stability of the XTR101AP are improved; the reverse connection preventing circuit is used for preventing the transmitter from being damaged when the polarity of an external circuit power supply is reversed.
Further, the cold end temperature compensation circuit may be provided to include a resistor R1, a resistor R2, a resistor R3, and a temperature sensor AD 590; the connection line of one end of the resistor R3 and the end B of the thermocouple is connected with the 10 pin of the XTR101AP in the XTR101AP conversion circuit, the connection line of the other end of the resistor R3 and one end of the resistor R2 is connected with the cathode of the temperature sensor AD590 and one end of the resistor R4 in the XTR101AP conversion circuit, the connection line of the anode of the temperature sensor AD590 and one end of the resistor R1 is connected with the 11 pin of the XTR101AP in the XTR101AP conversion circuit, and the connection line of the other end of the resistor R1 and the other end of the resistor R2 is connected with the 3 pin of the XTR101AP in the XTR101AP conversion circuit.
Further, the XTR101AP conversion circuit may be configured to include XTR101AP, resistor Rs, resistor R4, capacitor C1, and capacitor C2; wherein, 3 feet of XTR101AP is connected to the connecting line of a resistor R1 in the cold end temperature compensation circuit and a resistor R2 in the cold end temperature compensation circuit, one end of a capacitor C1 is grounded, the other end of a capacitor C1 is connected to the connecting line of a 4 foot of XTR101AP and the A end of the thermocouple, two ends of a resistor Rs are respectively connected with a 5 foot and a 6 foot of XTR101AP, one end of a resistor R4 is connected to the connecting line of a resistor R3 and a resistor R2 in the cold end temperature compensation circuit, a 7 foot of XTR101AP is connected with the negative end of an output end in the anti-reverse connection circuit and the other end of a resistor R4, a capacitor C2 is connected in parallel to two ends of a resistor R4, an 8 foot of XTR101AP is respectively connected with a resistor R6 in the current expanding circuit and the cathode of a diode D5 in the anti-reverse connection circuit, a 9 foot of XTR101AP is connected with the emitter of a triode Q1 in the current expanding circuit, a 10 foot of XTR AP is connected to the connecting line of a resistor R3 in the cold end temperature compensation circuit and the cold end AD temperature compensation circuit, a positive terminal of the cold end AD 63R 639 is connected with a positive terminal AD590, the 12 feet of XTR101AP is connected with the base of transistor Q1 in the current-expanding circuit.
Further, the current expanding circuit can be arranged to include a transistor Q1 and a resistor R6; one end of the resistor R6 is connected to a connection line of an 8 pin of the XTR101AP in the XTR101AP conversion circuit and a cathode of the diode D1 in the anti-reverse connection circuit, the other end of the resistor R6 is connected with a collector of the triode Q1, a base of the triode Q1 is connected with a 12 pin of the XTR101AP in the XTR101AP conversion circuit, and an emitter of the triode Q1 is connected with a 9 pin of the XTR101AP in the XTR101AP conversion circuit.
Further, the anti-reverse connection circuit can be arranged to comprise a diode D1, a capacitor C3, an output terminal positive terminal and an output terminal negative terminal; the connection line of the cathode of the diode D1 and the 8 pin of the XTR101AP in the XTR101AP conversion circuit is connected with a resistor R6 in the current-expanding circuit, the connection line of the anode of the diode D1 and the positive end of the output end is connected with one end of a capacitor C3, the other end of the capacitor C3 is connected with the connection line of the 7 pin of the XTR101AP in the XTR101AP conversion circuit and the negative end of the output end, and the positive end of the output end and the negative end of the output end are connected with an external circuit.
Further, can be provided withThe external circuit comprises a power supply V PS And a load R L Power supply V PS The positive terminal is connected with the positive terminal of the output terminal in the reverse-connection preventing circuit, and the power supply V PS Negative terminal grounded and connected with load R L One end, load R L The other end is connected with the negative end of the output end in the anti-reverse connection circuit.
Because high accuracy current type temperature sensor AD590 output current is directly proportional (1uA/K) with absolute temperature, consequently the utility model discloses utilize AD 590's accurate cold junction temperature electric current reposition of redundant personnel effect to make offset voltage along with temperature linear variation, overcome the defect of offset voltage along with temperature nonlinear variation when the diode is used as cold junction temperature compensation to realize accurate cold junction temperature compensation. The utility model discloses utilize temperature sensor AD590 to carry out thermocouple cold junction compensation circuit design innovatively, the temperature compensation precision is high, has improved the temperature measurement precision of changer greatly, and the performance is excellent, and is with low costs, and the circuit is simple easily to be realized.
The utility model discloses a theory of operation:
the utility model discloses design based on XTR101 AP's theory of operation, according to XTR101 AP's theory of operation, can learn following several points: (1) XTR101AP inputs the voltage difference e applied between pin 3 and pin 4 IN ＝e 2– e 1 The current I of 4-20mA is formed after the voltage amplification O Flows in the output loop between XTR101AP output pin 7 and pin 8 (through R) L 、V PS And D 1 ) (ii) a (2) Voltage e applied to input pin 3 of XTR101AP 1 Will appear on pin 5 of XTR101AP, similarly voltage e on XTR101AP input pin 4 2 Will appear on pin 6 of XTR101AP, and thus span-setting resistor R S Current I in S ＝(e 2 –e 1 )/R S ＝e IN /R S (ii) a (3) When e is IN When 1 is 0V O 4 mA; according to e IN By proper selection of R S Can make I O The upper limit of (b) corresponds to 20 mA; r S According to the output current I O With a variation range of 16mA and an input voltage e IN The full scale range of (c) is calculated, namely: (0.016+ 40/R) S )×(e IN Full scale) 16 mA; (4) due to I O Is unipolar, e 2 Must remain greater than e 1 (ii) a I.e. e IN Is more than or equal to 0. To limit the upper range I O Not more than 20mA, when R S Infinity, e IN Must remain less than 1V when R S When decreasing, e IN Must be scaled down.
Circuit schematic As shown in FIG. 1, if no thermocouple cold end compensation is performed (i.e., the A end of the thermocouple is connected directly to pin 4 of XTR101AP and the B end of the thermocouple is connected directly to pin 3 of XTR101 AP), then:
e IN ＝e (t-t0) instead of e IN ＝e t Wherein t is the temperature at the measuring end of the thermocouple, t 0 Is the thermocouple cold end temperature. Therefore, the output value of the transmitter has larger error with the temperature t detected by the thermocouple, and the error is along with the temperature t of the cold end 0 And the variation is even further increased. In order to improve the conversion precision of the transmitter, the cold end compensation of the thermocouple must be realized, the utility model discloses the cold end compensation circuit of unique innovation has been designed in XTR101 AP's application circuit.
As shown in the left half part of fig. 2 the utility model discloses cold junction temperature compensation + XTR101AP converting circuit, cold junction temperature compensation circuit comprises resistance R1, R2, R3 and temperature sensor AD590, utilizes the constant current source of pin 10 and the 11 outputs of pin of XTR101AP, forms cold junction compensation voltage. AD590 is a two-wire current mode integrated circuit temperature sensor, the output current of the two-wire current mode integrated circuit temperature sensor is proportional to absolute temperature, the output current increases by 1 muA when the temperature increases by 1K, the corresponding K temperature scale output is 1uA/K, and the output is 273.2+1 uA/DEG C when the temperature scale output is in centigrade. For detecting the cold-end temperature t of the thermocouple 0 And is converted into a current I t0 ＝I 1 ＝ 273.2+t 0 (uA)。
As shown on the right half of fig. 2, the utility model discloses cold junction temperature compensation circuit's equivalent voltage return circuit to this voltage return circuit: e.g. of the type IN +e R2 –e R3 –e (t-t0) 0, wherein: e.g. of the type IN Is the input voltage of XTR101 AP; e.g. of the type t The cold end of the thermocouple is 0 ℃, and the temperature of the measuring end is t; e.g. of a cylinder (t-t0) Is a thermocouple with cold end t 0 Measuring the thermoelectric potential when the temperature of the end is t; e.g. of the type R2 And e R3 Is the voltage developed across resistor R2 and resistor R3.
According to the thermoelectric potential principle of the thermocouple: e.g. of a cylinder (t-t0) ＝e t –e t0 ；
Therefore e IN ＝e R3 –e R2 +e t –e t0 ＝e t +(e R3 –e R2 –e t0 )；
Therefore, there should be e when the circuit fully (accurately) compensates the cold end temperature of the thermocouple IN ＝e t I.e. is e R3 –e R2 –e t0 ＝0；
This gives: should have thermocouple cold-end potential e t0 ＝e R3 –e R2 ；
Due to e R3 ＝1mA×R3，e R2 ＝I 2 ×R2＝(1–I 1 )×R2＝(1000–273.2–t 0 )×10 -3 mA×R2；
It follows that, as long as R2 and R3 are adjusted to appropriate values, one can achieve:
e t0 ＝e R3 -e R2 (ii) a I.e. e IN ＝e t (e IN Independent of cold end temperature, complete cold end temperature compensation)
Thus, the temperature compensation voltage e generated by the precise cold side temperature current splitting of AD590 R2 The characteristic of linear variation along with the temperature can accurately compensate the cold junction temperature t of the thermocouple 0 Eliminating cold end temperature t of thermocouple 0 The influence on the temperature measurement is completely compensated.
Other technical descriptions:
1. for applications requiring moderate accuracy, XTR101AP can operate very efficiently with only its internal drive transistors. For applications requiring higher requirements (high gain and high precision), an external NPN transistor Q1 can be added and connected in parallel with the internal transistor of XTR101AP in order to shunt the partial current of the internal transistor of XTR101AP, reduce the heat generation inside the XTR101AP package, reduce the temperature effect and improve the precision.
2. External circuit power supply V PS The range is as follows: the direct current is 12V-40V, and the typical application is 24 VDC.
3. Two-wire output load R L ：V PS When R is 24V, R L ＝0～600Ω；V PS When R is 40V, R L ＝0～1400Ω。
4. The diode D1 is used for power polarity reverse protection.
5、V PS And R L The power supply and the output load of the external circuit are connected according to the standard connection mode of the two-wire system transmitter.
6. R2, R3 and Rs are adjustable manganese copper wire resistors, and the resistance value is determined by the thermocouple type (graduation) and the measuring range (in the figure, the marked parameters are K-type thermocouples, and the upper limit of the temperature measuring range is 800 ℃ for example).
7. R4 is an input bias resistor, and 2mA current flows through the input bias resistor to form 2V input bias voltage; the capacitor C2 is a bias voltage decoupling (filter) capacitor.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (6)
1. The utility model provides a take two-wire system thermocouple temperature transmitter of cold junction temperature compensation which characterized in that: the temperature compensation circuit comprises a cold end temperature compensation circuit and an XTR101AP conversion circuit; the A end of the thermocouple is connected with the XTR101AP conversion circuit, the B end of the thermocouple is connected with the cold end temperature compensation circuit and the XTR101AP conversion circuit, and the XTR101AP conversion circuit is also connected with the cold end temperature compensation circuit.
2. The two-wire thermocouple temperature transmitter with cold end temperature compensation of claim 1, wherein: further comprising: the current expanding circuit is connected with the XTR101AP conversion circuit and the reverse connection preventing circuit, and the reverse connection preventing circuit is further connected with the XTR101AP conversion circuit.
3. The two-wire thermocouple temperature transmitter with cold end temperature compensation of claim 1, wherein: the cold end temperature compensation circuit comprises a resistor R1, a resistor R2, a resistor R3 and a temperature sensor AD 590; the connection line of one end of the resistor R3 and the end B of the thermocouple is connected with the 10 pin of the XTR101AP in the XTR101AP conversion circuit, the connection line of the other end of the resistor R3 and one end of the resistor R2 is connected with the negative electrode of the temperature sensor AD590 and one end of the resistor R4 in the XTR101AP conversion circuit, the connection line of the positive electrode of the temperature sensor AD590 and one end of the resistor R1 is connected with the 11 pin of the XTR101AP in the XTR101AP conversion circuit, and the connection line of the other end of the resistor R1 and the other end of the resistor R2 is connected with the 3 pin of the XTR101AP in the XTR101AP conversion circuit.
4. The two-wire thermocouple temperature transmitter with cold end temperature compensation of claim 1, wherein: the XTR101AP conversion circuit comprises an XTR101AP, a resistor Rs, a resistor R4, a capacitor C1 and a capacitor C2; the 3 feet of the XTR101AP are connected to a connecting line of a resistor R1 in the cold-end temperature compensation circuit and a resistor R2 in the cold-end temperature compensation circuit, one end of a capacitor C1 is grounded, the other end of the capacitor C1 is connected to a connecting line of a 4 foot of the XTR101AP and the A end of the thermocouple, two ends of a resistor Rs are respectively connected with a 5 foot and a 6 foot of the XTR101AP, one end of the resistor R4 is connected to a connecting line of a resistor R3 and a resistor R2 in the cold-end temperature compensation circuit, a 7 foot of the XTR101AP is connected with the other end of a resistor R4, the capacitor C2 is connected in parallel to two ends of the resistor R4, a 10 foot of the XTR101AP is connected to a connecting line of a resistor R3 and the B end of the cold-end temperature compensation circuit, and an 11 foot of the XTR101AP is connected to a connecting line of a positive electrode and a resistor R1 of a temperature sensor AD590 in the cold-end temperature compensation circuit.
5. The two-wire thermocouple temperature transmitter with cold end temperature compensation of claim 2, wherein: the current expansion circuit comprises a triode Q1 and a resistor R6; one end of the resistor R6 is connected to a connection line between the pin 8 of the XTR101AP in the XTR101AP conversion circuit and the cathode of the diode D1 in the anti-reverse connection circuit, the other end of the resistor R6 is connected with the collector of the triode Q1, the base of the triode Q1 is connected with the pin 12 of the XTR101AP in the XTR101AP conversion circuit, and the emitter of the triode Q1 is connected with the pin 9 of the XTR101AP in the XTR101AP conversion circuit.
6. The two-wire thermocouple temperature transmitter with cold end temperature compensation of claim 2, wherein: the reverse connection preventing circuit comprises a diode D1, a capacitor C3, an output end positive end and an output end negative end; the connection line of the cathode of the diode D1 and the 8 pin of the XTR101AP in the XTR101AP conversion circuit is connected with a resistor R6 in the current-expanding circuit, the connection line of the anode of the diode D1 and the positive end of the output end is connected with one end of a capacitor C3, the other end of the capacitor C3 is connected with the connection line of the 7 pin of the XTR101AP in the XTR101AP conversion circuit and the negative end of the output end, and the positive end of the output end and the negative end of the output end are connected with an external circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202220874064.4U CN217358783U (en) | 2022-04-15 | 2022-04-15 | Two-wire system thermocouple temperature transmitter with cold end temperature compensation |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202220874064.4U CN217358783U (en) | 2022-04-15 | 2022-04-15 | Two-wire system thermocouple temperature transmitter with cold end temperature compensation |
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| CN217358783U true CN217358783U (en) | 2022-09-02 |
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|---|---|---|---|
| CN202220874064.4U Expired - Fee Related CN217358783U (en) | 2022-04-15 | 2022-04-15 | Two-wire system thermocouple temperature transmitter with cold end temperature compensation |
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