CN102661814A - Thermocouple temperature transmitter and realizing method - Google Patents

Abstract

The invention relates to a thermocouple temperature transmitter and a realizing method. The thermocouple temperature transmitter is characterized by comprising a K type thermocouple, a K type thermocouple signal processing integrated circuit, a single chip and a TTL/RS485 level switching circuit which are connected in turn; an indexing table for the K type thermocouple is stored in the single chip; a thermoelectromotive force value is calculated by the single chip by reading an analog-to-digital conversion result of the K type thermocouple signal processing integrated circuit; the indexing table for the K type thermocouple is looked up and a temperature value is accurately calculated according to a linear interpolation method; and the temperature value is outputted in a serial mode. The thermocouple temperature transmitter has the advantages that: software is used for compensating nonlinearity of the thermocouple, the temperature value is outputted in a digital value serial mode, the error caused by an analog signal during a transmission process is eliminated and the measurement precision is increased.

Description

A kind of thermocouple temperature transmitter and implementation method

Technical field

The invention belongs to the temperature survey field, be specifically related to a kind of transmitter that utilizes thermocouple measuring temperature.

Background technology

The common serviceability temperature transmitter of the measurement of industrial process temperature, high temperature measurement generally uses thermocouple temperature transmitter at present, and transmitter is output as analog electrical signal, and standards such as 4～20mA, 1～5V, 0～5V are arranged.Because the thermopower that thermopair produces is the mV order of magnitude; And and relation is non-linear between the temperature, needs to amplify and nonlinear compensation, because environment temperature is not 0 ℃; Also need cold junction compensation; Thermocouple temperature transmitter in the market, inside is mimic channel, becomes to send precision not high; The simulating signal of output is vulnerable to disturb in transmission simultaneously, after signal passes to measuring and controlling equipment, also need convert digital signal into.

Summary of the invention

The objective of the invention is to solve the problem that exists in the background technology, it is the temperature transmitter of sensor that a kind of K of employing type thermopair is provided, and it adopts software that the non-linear of thermopair compensated, and direct output temperature digital value.

The present invention is achieved in that a kind of thermocouple temperature transmitter, it is characterized in that: comprise K type thermopair, K type thermocouple signal processing integrated circuit, single-chip microcomputer, TTL/RS485 level shifting circuit.

Described K type thermocouple signal processing integrated circuit is connected with K type thermopair, is used for the mould/number conversion of K type thermocouple cold junction compensation, thermopower.

Described single-chip microcomputer is connected with K type thermocouple signal processing integrated circuit; Be used to read the data that the mould/number conversion of K type thermocouple signal processing integrated circuit goes out; Calculate the thermopower value of K type thermopair; Look into K type thermocouple indexing table, accurately calculate Temperature numerical, and export with serial mode with linear interpolation method.

Described TTL/RS485 level shifting circuit is connected with single-chip microcomputer, is used for converting the Transistor-Transistor Logic level of single-chip microcomputer output into the RS485 level.

The present invention compared with prior art, advantage is: adopt software that the non-linear of thermopair compensated, with digital quantity form serial output temperature numerical value, eliminated the error that simulating signal causes in transmission, improved measuring accuracy.

Description of drawings

Fig. 1 is the circuit theory diagrams of the embodiment of the invention;

Fig. 2 is the subroutine flow chart of the embodiment of the invention;

Fig. 3 is the main program flow chart of the embodiment of the invention.

Among Fig. 1: 1.K type thermopair; 2.K type thermocouple signal processing integrated circuit; 3. single-chip microcomputer; 4.TTL/RS485 level shifting circuit.

Embodiment

With reference to the accompanying drawings the embodiment of the invention is described in further detail.

A kind of thermocouple temperature transmitter shown in accompanying drawing 1, comprises K type thermopair 1, K type thermocouple signal processing integrated circuit 2, single-chip microcomputer 3, TTL/RS485 level shifting circuit 4.

The MAX6675 that K type thermocouple signal processing integrated circuit 2 optional U.S. MAXIM companies produce; Its inside has cold junction compensation; The thermopower A/D converter; Can convert the thermopower value to 12 bits, through SPI serial port output, the relation of thermopower and the data of changing out: the data * 10.25 μ V (10.25 μ V/LSB) of thermopower value=change out.

In the accompanying drawing 1, U1 is MAX6675, and "+" of K type thermopair, "-" end is connected with " T+ ", " T-" end of MAX6675 respectively, MAX6675 cs, SCK, SO (SPI serial port) be connected with 3 I/O pins of single-chip microcomputer respectively.

Single-chip microcomputer 3 optional inside are integrated with 8 or 32 single-chip microcomputers of FlashROM, EEPROM.

In the accompanying drawing 1, U2 is a single-chip microcomputer 3, model STC15F104E, and its inside is integrated with 4KB FlashROM, 1KBEEPROM and clock, reset circuit, and 8 pins are externally arranged.

The branch kilsyth basalt of K type thermopair is stored in the FlashROM storer of single-chip microcomputer 3.Adopt 1 ℃ K type thermocouple indexing table at interval, 0～1023 ℃ of temperature range, per 1 thermopower data are 16 bits in the table, wherein store the integral parts that millivolt is worth for 6,10 fraction parts that the storage millivolt is worth.For example: the thermopower value that temperature is 500 ℃ is 20.644mv, and the integral part of millivolt value is 20, corresponding binary number: 010100; The fraction part 644 of millivolt value, corresponding binary number: 1010000100, its storage signal is as follows.

Above-mentioned 0～1023 ℃ branch kilsyth basalt is deposited with constant array form, takies 3 interior FlashROM 2KB of single-chip microcomputer space.

Use 1 I/O pin (P3.0) simulation serial output interface of single-chip microcomputer 3 among the embodiment, output format is 10 of frame data: 1 start bit, 8 data bit, 1 position of rest, and baud rate 1200bps, every delivery time is 833 μ S.Accompanying drawing 2 is exported the subroutine flow chart of a byte number for serial.

In the accompanying drawing 1, U3 is a TTL/RS485 level shifting circuit 4, and model is MAX487; The DI pin of MAX487 is the Transistor-Transistor Logic level input end; Link to each other with the simulation serial output pin (P3.0) of single-chip microcomputer 3, the pin A of MAX487, B are the RS485 level output end, are connected with measuring and controlling equipment through connection terminal J1; R1 is a build-out resistor in the accompanying drawing 1, and resistance is 120 Ω.

In the accompanying drawing 1, the power supply of MAX6675, STC15F104E, MAX487 all adopts the power supply of direct current 5V power supply.

Accompanying drawing 3 is a main program flow chart, and a kind of implementation method of thermocouple temperature transmitter mainly may further comprise the steps:

Step 1: read the thermopower mould/number conversion numerical value of MAX6675 output by single-chip microcomputer, be kept among the variable TData; Utilize formula: Calculate thermopower value E _x

Step 2: table look-up and confirm E _xPosition in K type thermocouple indexing table obtains E _xFront and rear side dividing value E ₀, E ₁, and E ₀Pairing temperature value T ₀

For example:, calculate E if TData is 2443 _x=25.041mV;

Table look-up E ₀Be 25.033mV (603 ℃), E ₁Be 25.075mV (604 ℃);

Step 3: utilize linear interpolation formula

to calculate measured temperature values;

(going up example calculates: T=603.19 ℃)

Step 4: 1 the I/O pin (P3.0) through single-chip microcomputer is with baud rate 1200bps serial output temperature value T, 2 bytes of integral part, 1 byte of fraction part.

Claims (3)

1. thermocouple temperature transmitter is characterized in that:

(1) comprises K type thermopair (1), K type thermocouple signal processing integrated circuit (2), single-chip microcomputer (3), TTL/RS485 level shifting circuit (4);

(2) adopt the power supply of direct current 5V power supply, with serial mode output temperature numerical value;

(3) model of described K type thermocouple signal processing integrated circuit (2) is MAX6675; K type thermopair (1) is connected with the 2nd, 3 pins of MAX6675; 5,6,7 pins of MAX6675 are connected with 3 I/O pins of single-chip microcomputer (3), and 1 I/O pin of single-chip microcomputer (3) is connected with TTL/RS485 level shifting circuit (4);

(4) store K type thermocouple indexing table among inner FlashROM of described single-chip microcomputer (3) sheet or the EEPROM.

2. a kind of thermocouple temperature transmitter according to claim 1; It is characterized in that: K type thermocouple indexing table location mode is: per 1 thermopower data are 16 bits; Wherein the integral part of 6 storage millivolt values is stored millivolt fraction parts of value for 10.

3. the implementation method of a kind of thermocouple temperature transmitter according to claim 1 and 2 is characterized in that may further comprise the steps:

Step 1: read the thermopower mould/number conversion value of MAX6675 output, be kept among the variable TData; Utilize formula:

Calculate thermopower value E _x

Step 2: table look-up and confirm E _xPosition in K type thermocouple indexing table obtains E _xFront and rear side dividing value E ₀, E ₁, and E ₀Pairing temperature value T ₀

Step 3: utilize linear interpolation formula

to calculate measured temperature values.

Step 4: through 1 I/O pin serial output temperature value T of single-chip microcomputer.

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