Thermocouple temperature transmitter

1 basic profile editing

It consists of a reference source, cold-junction compensation, amplifying unit, linearization, V/I conversion, burn-out processing, reverse connection protection, and current limiting protection. It is the thermal potential generated by the thermocouple through the cold-end compensation after amplification, and then cap the linear circuit to eliminate the thermal potential and temperature of the nonlinear error, and finally amplified into 4 ~ 20mA current output signal. In order to prevent accidents caused by temperature control failure due to galvanic disconnection in thermocouple measurement, a power failure protection circuit is also provided in the transmitter. When the thermocouple breaks or fails to connect properly, the transmitter will output the maximum value (28mA) to make the meter cut off the power.

2 temperature transmitter principle edit

A temperature transmitter is a meter that converts a temperature variable to a standardized output signal that can be transmitted. It is mainly used for the measurement and control of industrial process temperature parameters.

Transmitters with sensors usually consist of two parts: sensors and signal converters. The sensors are mainly thermocouples or thermal resistors; the signal converters are mainly composed of measuring units, signal processing and conversion units (since the industrial thermal resistance and thermocouple index tables are standardized, the signal converters are also known as independent products. Transmitters) Some transmitters have additional display units and some also have fieldbus functionality. As the right picture:

Temperature transmitter schematic

If the transmitter consists of two sensors for measuring the temperature difference, there is a given continuous function relationship between the output signal and the temperature difference. It is called a temperature transmitter.

There is a given continuous function relationship (usually a linear function) between the output signal of the transmitter and the temperature variable, and the output signal of the early production transmitter has a linear function relationship with the resistance value (or voltage value) of the temperature sensor. .

The standardized output signals are mainly 0mA~10mA and 4mA~20mA (or 1V~5V) DC signals. Other standardized output signals with special regulations are not excluded.

Temperature transmitter can be divided into two-wire system and four-wire system according to the power supply wiring.

Transmitter has electric unit combination meter series (DDZ-II type, DDZ-III type and DDZ-S type) and miniaturized modular type, multifunctional intelligent type. The former does not have a sensor, and the latter two types of transmitters can be easily combined with a thermocouple or a thermal resistor to form a sensor-equipped transmitter.

3 Technical data editing input signal:

Thermocouples: k, e, j, b, s, t, n. Thermal resistance: pt100, cu50, cu100 three-wire system, four-wire system. The input signal of the intelligent temperature transmitter can be arbitrarily set by the handset and the PC;

output signal:

The 4-20mA DC signal is output within the measuring range, linear with the thermocouple or RTD input signal or linear with the temperature. Intelligent temperature transmitter output 4-20ma DC signal at the same time superimposed in accordance with the Hart standard protocol communication; Isolated temperature transmitter: input and output isolation, isolation voltage 500v, increased resistance to common-mode interference, more suitable for connecting with the computer Web use;

Basic error:

0.5%fs, 0.2%fs, intelligent 0.2%fs;

Wiring:

Two-wire system, three-wire system, four-wire system;

Display method:

Four LCD display on-site temperature, intelligent four-digit LCD can be used by pc or handheld

Set the instrument to display any of the parameters of field temperature, sensor value, output current, and percentage;

Operating Voltage:

Ordinary model 12v-35v, intelligent 12v-45v, rated operating voltage 24v

Allowed load resistance:

500Ω (24vdc power supply); limit load resistance r (max) = 50vmin-12, for example, at a rated operating voltage of 24v, the load resistance can be selected within the range of 0-600ω.

working environment:

a: Ambient temperature -25-+80°C (conventional type)

-25-+70°C (digital display type)

-25-+75°C (smart)

b: Relative humidity: 5%-95%

c: mechanical vibration f ≤ 50hz, amplitude ≤ 0.15mm

d: No corrosive gas or similar environment;

9. Environmental Impact Factor: δ ≤ 0.05%/°C.

4 main features edit

Simple structure: no moving or elastic components, so high reliability and minimal maintenance.

Easy to install: The built-in structure shows this feature in particular, without any special tools.

Easy to adjust: The zero and range potentiometers can perform any zero point shift or range change within the valid range of temperature detection. The two adjustments will not affect each other.

Widely used; suitable for liquid level measurement of high temperature, high pressure, strong corrosion and other media.

Main Specifications

Accuracy: 0.5, 1, 1.5

Pressure range: negative pressure, normal pressure, high pressure (32MPa or less)

Applicable medium: acid, alkali, salt or any medium without corrosion to PTFE

Output signal: 4-20mA, two-wire system

Power supply: load resistance 0-750Ω DC24V

Fixing method: Thread mounting M20×1.5, M27×2 Flange mounting DN15, DN25, DN50, DN80.

5 selection data editing

Z

Thermal resistance

M

Nickel-chromium-silicon-nickel-chromium

N

Nickel-Chromium-Nickel Silicon

E

Nickel-chromium-copper nickel

F

Iron - Copper Nickel

C

Copper-copper nickel

P

platinum

C

copper

B

Temperature Transmitter

1

No fixture

2

Fixed thread

3

Movable flange

4

Fixed flange

5

Active connection type

6

Fixed thread taper

7

Straight pipe joint type

8

Fixed thread fittings

9

Active thread coupling

2

Blowout type

3

Waterproof

4

Explosion-proof

0

Ф16

1

Ф12

2

Ф16 high aluminum tube

3

Ф20 high aluminum tube

G

Variable section

M

Analog display

S

Digital Display

no

Normal installation

Z

Separate installation

W

R

N

B

2

4

0

G

S

Z

6 equipment maintenance editor

The indicator indicates abnormal phenomenon, such as indication high, low, no change or no confusion, etc., itself contains two factors: First, process factors, RTD temperature transmitter instrument truly reflects the abnormal process; The second is the instrument factor, because the meter measurement system fault appears in a certain direction. The following inspection process is limited to instrument system failures. When the fault source is determined to be a non-technical problem, it is checked in accordance with the fault determination procedure to eliminate the instrument fault.

If the meter records a dead line (a line with no changes in the line is called a dead line), or the record curve originally fluctuates, it suddenly becomes a direct thermal resistance temperature transmitter line; the failure is likely to be in the instrument system. Because the recording instruments are mostly DCS computer systems, the sensitivity is very high, and the changes in the parameters can be reflected very sensitively. At this point can artificially change the process parameters to see the curve changes. If it does not change, the basic conclusion is that the instrument system has a problem; if there is a normal change, the base thermal resistance temperature transmitter determines that the instrument system has no major problems.