CN212363473U - Cold end compensation device for PLC thermocouple module - Google Patents
Cold end compensation device for PLC thermocouple module Download PDFInfo
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- CN212363473U CN212363473U CN202020981293.7U CN202020981293U CN212363473U CN 212363473 U CN212363473 U CN 212363473U CN 202020981293 U CN202020981293 U CN 202020981293U CN 212363473 U CN212363473 U CN 212363473U
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Abstract
The utility model provides a cold junction compensation arrangement for PLC thermocouple module, include: the method comprises the steps of adopting an internal compensation wiring method, adding a first RTD sensor, a second RTD sensor, a first analog switch, a second analog switch, a third analog switch and a thermocouple acquisition chip in a thermocouple module, wherein the first RTD sensor is located at one end of a temperature measurement channel wiring terminal of the thermocouple module, the second RTD sensor is located at the other end of the temperature measurement channel wiring terminal of the thermocouple module, and utilizing the first RTD sensor and the second RTD sensor to measure the cold junction temperature of the thermocouple module.
Description
Technical Field
The utility model relates to a thermocouple technical field, in particular to cold junction compensation arrangement for PLC thermocouple module.
Background
The thermocouple module of the PLC adopts the thermocouple sensor to realize temperature acquisition and monitoring, and for the thermocouple sensor, the temperature compensation of the cold junction directly influences the temperature measurement precision of the sensor. The cold end compensation method for the PLC thermocouple module at present can be mainly divided into external compensation and internal compensation.
External compensation is usually by a compensation wire method. The compensation wire method is based on the principle that one end of the compensation wire is connected to the cold end of the thermocouple and the other end of the compensation wire is connected to the wiring terminal of the PLC thermocouple module by utilizing the law of the middle conductor of the thermocouple. Meanwhile, the cold end temperature of the thermocouple needs to be kept constant, or the cold end temperature of the thermocouple needs to be measured by using an RTD (real time detector) to compensate the cold end temperature. The method has the disadvantages that the price of the compensating lead is high, the wiring of the module is complicated, and the use is inconvenient.
The internal compensation is to directly connect the cold end of the thermocouple to the wiring terminal of the PLC thermocouple module, then add a temperature measurement chip in the module, and directly compensate the temperature collected by the temperature measurement chip as the cold end temperature. This method is generally subject to large errors.
SUMMERY OF THE UTILITY MODEL
The purpose of the present invention is to solve at least one of the technical drawbacks.
Therefore, the utility model aims to provide a cold junction compensation arrangement for PLC thermocouple module.
In order to achieve the above object, an embodiment of the present invention provides a cold junction compensation device for a PLC thermocouple module, including:
adopting a wiring method of internal compensation, adding a first RTD sensor, a second RTD sensor, a first analog switch, a second analog switch, a third analog switch and a thermocouple acquisition chip in a thermocouple module, wherein the first RTD sensor is positioned at one end of a temperature measurement channel wiring terminal of the thermocouple module, the second RTD sensor is positioned at the other end of the temperature measurement channel wiring terminal of the thermocouple module, and measuring the temperature of a cold end of the thermocouple module by using the first RTD sensor and the second RTD sensor;
when the thermocouple module works normally, the wiring terminal is vertical to the ground, and the first RTD sensor is positioned right above the second RTD sensor;
the first RTD sensor and the second RTD sensor are connected with the first analog switch and the second analog switch, so that the first analog switch and the second analog switch three cold end compensation differential input channels and a reference input channel, and the third analog switch switches three channels of constant current sources required by cold end compensation;
the thermocouple acquisition chip is connected with the first RTD sensor and the second RTD sensor and used for providing two paths of constant current sources for the RTD channels and the reference input channel of the first RTD sensor and the second RTD sensor.
Further, the first analog switch, the second analog switch and the third analog switch adopt a low-voltage CMOS analog multiplexer with the model number of ADG 709.
Further, the first RTD sensor and the second RTD sensor are connected as follows: the input adopts a 2-wire wiring, the differential signal is input, one path of differential signal is connected with two ends of a first transient suppression diode through a group of filter capacitors, two sides of the first transient suppression diode are further respectively connected with a second transient suppression diode and a third transient suppression diode, one side of the first transient suppression diode is further connected to a reference resistor through a first resistor, the other side of the first transient suppression diode is further connected to the reference resistor through a second resistor, one side of the reference resistor is connected with the cathode of the first diode and the anode of the second diode and further connected with the cathode of the third diode, and the anode of the third diode is used as an output end.
According to the utility model discloses a cold junction compensation arrangement for PLC thermocouple module adopts the RTD of two way 2 line systems directly to obtain the inside cold junction compensation temperature of module or two wherein passageways of collector of a plurality of thermocouple temperature measurement passageways, and the cold junction temperature of all the other passageways is through calculating out.
Compare the outside and the inside compensation method of current PLC thermocouple module cold junction, the utility model has the following characteristics:
1) the wiring mode of internal compensation is adopted, so that complicated wiring and using methods of external compensation are avoided;
2) the RTD is used for measuring the temperature internally, a compensation lead is omitted, and compared with external compensation, the cost is lower;
3) according to inside RTD1 to the cold junction temperature of the rule compensation of temperature variation between RTD2, compare in the mode with the inside compensation of temperature measurement chip, the precision is higher, and is more reliable.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
fig. 1 is a schematic diagram of a cold end compensation arrangement for a PLC thermocouple module according to an embodiment of the present invention;
fig. 2a and 2b are circuit diagrams of a 2-way RTD sensor acquiring an internal cold end temperature channel according to an embodiment of the present invention;
fig. 3a to 3c are circuit diagrams of three-way cold end compensation differential channel switching according to an embodiment of the present invention;
fig. 4 is a circuit diagram of RTD measurement according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present invention, and should not be construed as limiting the present invention.
In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "fixed" are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.
As shown in fig. 1, the utility model discloses a cold junction compensation arrangement for PLC thermocouple module 100, include: adopt the wiring method of internal compensation, add first RTD sensor RTD1 and second RTD sensor RTD2 in thermocouple module 100 inside, first analog switch, second analog switch and third analog switch, the chip is gathered to the thermocouple, first RTD sensor RTD1 is located thermocouple module 100 temperature measurement passageway binding post 300's one end, second RTD sensor RTD2 is located thermocouple module 100 temperature measurement passageway binding post 300's the other end, utilize first RTD sensor RTD1 and second RTD sensor RTD2 to measure thermocouple module 100's cold junction temperature.
The invention adopts a wiring method of internal compensation, and is different in that two RTDs are added in a thermocouple module 100 and used for measuring the temperature of a cold end of a thermocouple, and the two RTDs are respectively positioned at two ends of a module temperature measuring channel wiring terminal 300.
In an embodiment of the present invention, as shown in fig. 2 a-2 b, the first RTD sensor RTD1 and the second RTD sensor RTD2 are connected as follows: the input adopts a 2-wire wiring, the differential signal is input, one path of differential signal is connected with two ends of a first transient suppression diode through a group of filter capacitors, two sides of the first transient suppression diode are further respectively connected with a second transient suppression diode and a third transient suppression diode, one side of the first transient suppression diode is further connected to a reference resistor through a first resistor, the other side of the first transient suppression diode is further connected to the reference resistor through a second resistor, one side of the reference resistor is connected with the cathode of the first diode and the anode of the second diode and further connected with the cathode of a third diode, and the anode of the third diode is used as an output end.
Fig. 2a to 2b represent that 2 RTD sensors acquire internal cold end temperature channels, cold end temperatures of the other channels are calculated by directly measuring the acquired 2 internal cold end temperatures, the JT1 and JT2 sensors are connected by 2 wires and added with filter capacitors, the measurement mode adopts a constant current source and a proportional method, R98 and R110 adopt high-precision resistors as reference resistors, and RTD signal input and reference signal input are both differential signals.
The first RTD sensor RTD1 and the second RTD sensor RTD2 are connected with the first analog switch and the second analog switch, so that the first analog switch and the second analog switch three paths of cold end compensation differential input channels and reference input channels, and the third analog switch switches three paths of cold end compensation required constant current source channels.
In an embodiment of the present invention, the first analog switch, the second analog switch and the third analog switch employ a low voltage CMOS analog multiplexer model ADG709, as shown in fig. 3a to 3 c. The first analog switch U27 and the second analog switch U28 in fig. 3 a-3 c switch the three-way cold-side compensated differential input channel and the reference input channel: the external RTD, the internal RTD1 and the internal RTD2, and the third analog switch U29 switches the channels of the constant current source required by the 3-path cold-end compensation;
in fig. 1, two internal RTDs measure the temperature at both ends of the connection terminal 300, respectively. The switching of the analog switches in fig. 3a to 3c makes the present invention compatible with conventional external RTD cold-side compensation.
The thermocouple acquisition chip is connected with the first RTD sensor RTD1 and the second RTD sensor RTD2 and is used for providing two paths of constant current sources for RTD channels and reference input channels of the first RTD sensor RTD1 and the second RTD sensor RTD 2.
In the thermocouple acquisition chip adopted in fig. 4, the signal input is a differential signal, and two paths of constant current sources are provided for the RTD channel and the reference input channel.
In normal operation of the thermocouple module 100, the terminal 300 is perpendicular to the ground, and the first RTD sensor RTD1 is located directly above the second RTD sensor RTD2, i.e., RTD1 is directly above RTD 2. The temperature near the RTD1 is inevitably higher than that of the RTD2 due to the self-operation heating of the module, the temperature between the RTD1 and the RTD2 is also gradually reduced, and when an internal compensation wiring method is adopted, the temperature change rule is also the change rule of the cold end temperature of the thermocouple. Therefore, the cold end temperature of the thermocouples of all channels can be calculated according to the temperature change rule and the temperature values measured by the RTDs 1 and 2, and compensation is further performed.
The temperature change rule between the RTD1 and the RTD2 is an important factor influencing the compensation accuracy of the invention, and the rule is mainly related to the heating condition of the PCB of the module and needs to be determined through experiments.
According to the utility model discloses a cold junction compensation arrangement for PLC thermocouple module adopts the RTD of two way 2 line systems directly to obtain the inside cold junction compensation temperature of module or two wherein passageways of collector of a plurality of thermocouple temperature measurement passageways, and the cold junction temperature of all the other passageways is through calculating out.
Compare the outside and the inside compensation method of current PLC thermocouple module cold junction, the utility model has the following characteristics:
1) the wiring mode of internal compensation is adopted, so that complicated wiring and using methods of external compensation are avoided;
2) the RTD is used for measuring the temperature internally, a compensation lead is omitted, and compared with external compensation, the cost is lower;
3) according to inside RTD1 to the cold junction temperature of the rule compensation of temperature variation between RTD2, compare in the mode with the inside compensation of temperature measurement chip, the precision is higher, and is more reliable.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Although embodiments of the present invention have been shown and described, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that changes, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art without departing from the principles and spirit of the present invention. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (3)
1. A cold junction compensation device for a PLC thermocouple module is characterized in that an internal compensation wiring method is adopted, a first RTD sensor, a second RTD sensor, a first analog switch, a second analog switch, a third analog switch and a thermocouple acquisition chip are added in the thermocouple module, the first RTD sensor is located at one end of a temperature measurement channel wiring terminal of the thermocouple module, the second RTD sensor is located at the other end of the temperature measurement channel wiring terminal of the thermocouple module, and the cold junction temperature of the thermocouple module is measured by the first RTD sensor and the second RTD sensor;
when the thermocouple module works normally, the wiring terminal is vertical to the ground, and the first RTD sensor is positioned right above the second RTD sensor;
the first RTD sensor and the second RTD sensor are connected with the first analog switch and the second analog switch, so that the first analog switch and the second analog switch three cold end compensation differential input channels and a reference input channel, and the third analog switch switches three channels of constant current sources required by cold end compensation;
the thermocouple acquisition chip is connected with the first RTD sensor and the second RTD sensor and used for providing two paths of constant current sources for the RTD channels and the reference input channel of the first RTD sensor and the second RTD sensor.
2. The cold end compensation apparatus for a PLC thermocouple module of claim 1, wherein the first, second and third analog switches employ a low voltage CMOS analog multiplexer model ADG 709.
3. The cold end compensation apparatus for a PLC thermocouple module of claim 1, wherein the first RTD sensor and the second RTD sensor are connected as follows: the input adopts a 2-wire wiring, the differential signal is input, one path of differential signal is connected with two ends of a first transient suppression diode through a group of filter capacitors, two sides of the first transient suppression diode are further respectively connected with a second transient suppression diode and a third transient suppression diode, one side of the first transient suppression diode is further connected to a reference resistor through a first resistor, the other side of the first transient suppression diode is further connected to the reference resistor through a second resistor, one side of the reference resistor is connected with the cathode of the first diode and the anode of the second diode and further connected with the cathode of the third diode, and the anode of the third diode is used as an output end.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020981293.7U CN212363473U (en) | 2020-06-02 | 2020-06-02 | Cold end compensation device for PLC thermocouple module |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020981293.7U CN212363473U (en) | 2020-06-02 | 2020-06-02 | Cold end compensation device for PLC thermocouple module |
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| CN212363473U true CN212363473U (en) | 2021-01-15 |
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| CN202020981293.7U Active CN212363473U (en) | 2020-06-02 | 2020-06-02 | Cold end compensation device for PLC thermocouple module |
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