Why thermocouple temperature compensation, compensation method have

Thermocouple is negative, compensation conductor is divided into positive and negative, connection, first configure it. In the run. Common with short circuit, open circuit, poor contact and metamorphism. Checks, to make a thermocouple is separated from the secondary table with tools short compensation line in the second table, table indicating at room temperature and sub thermocouple terminals, thermocouple in the ambient temperature (table batch No, compensation wire fault) That measure roughly with a multimeter mv file thermocouple thermoelectric potential. The cold end temperature method

general thermocouple calibration cold end temperature 0 ℃ as standard. So, often to the cold end put in ice water, to keep the temperature for the constant 0 ℃. Under laboratory conditions, usually put the cold end of insulating oil have a test tube, and then put it in the heat preservation container full of ice water, is to maintain 0 ℃ cold end. Cold end temperature correction method

as a result of the thermocouple temperature indexing table is in the cold end temperature keep under 0 ℃, and its supporting the use of measuring circuit or display instrument is according to the calibration curve, so the cold end temperature is not equal to 0 ℃, we have to modify it indicates a value on the instrument. Such as the cold end temperature above 0 ℃, but constant in the t0 ℃, the measured less than the thermocouple thermoelectric ShiYao index value, as the real temperature, available laws of the intermediate temperature, under the box type modification:

E ( t, 0) = E ( t, t1) + E ( t1, 0) Method of compensating conductor

in order to make the thermocouple cold junction temperature constant ( It is best to 0 ℃) , the thermocouple can be done for a long, cold end away from work, and together with the measuring instrument to constant temperature or temperature fluctuations are small. But this method make inconvenient installation and use, and can take a lot of precious metal materials. Therefore, the use of a general called compensation conductor cable will radiate thermocouple cold end. This lead to a certain temperature range, 0～150℃） Has the same thermoelectric properties and the connected thermocouple, if use cheap thermocouple made of metal, usable material itself as compensation conductor, to extend the cold end to the temperature constant.

compensation conductor should be attention in the use of

( 1) The choice of the compensating conductor

compensation conductor must according to the type of thermocouple used properly choose and use occasion. K type should I choose k type, for example, accidentally compensating lead wires, according to the using situation, choose the operating temperature range. Usually work temperature for - kx 20 ~ 100 ℃, wide range of for - 25～200℃。 Common error of plus or minus 2. Level 5 ℃, the precision of plus or minus 1. 5℃。

( 2) Contact between

and thermocouple closer to terminal 2 contact as soon as possible, try to keep two junction temperature. And meter terminal junction temperature consistent as far as possible, instrument cabinets have a fan, don't make contact place to protect the fan blowing straight to contact.

（ 3) Using length

because of thermocouple signal is very low, for microvolt level, if you use the distance is too long, the signal attenuation and the interference of high-voltage electrical coupling in the environment, can make the thermocouple signal distortion, cause inaccurate measurement and control temperature, serious when produce temperature fluctuations in the control.

according to our experience, usually use the length of the thermocouple compensation wire control within 15 meters is better, if more than 15 meters, it is recommended to use temperature transmitter to transmit signal. Temperature transmitter is the potential value of the corresponding temperature is converted into direct current stream, strong anti-jamming.

( 4) Wiring

the compensating conductor wiring must be far away from power lines and interference sources. Where can't avoid crossing, also adopts cross method, as far as possible not parallel.

( 5) Shielding compensation conductor

in order to improve the anti-interference of thermocouple wire, shielding compensation conductor can be used. For the interference sources more occasions, the effect is better. Strictly grounding, but must will shield or shield does not have the effect of shielding, enhance interference instead. Compensation bridge bridge

compensation method is to use the voltage produced by the unbalanced bridge to compensate for the thermocouple thermoelectric potential caused by the cold end temperature and changes in value. Compensation bridge has been standardized. Unbalanced bridge ( The compensation bridge) Is composed of resistor R1, R2, R3 and RCu. The R1 = R2 = R3 = 1; The Rs is made of temperature coefficient is small manganese copper wire winding and become; RCu is temperature coefficient is larger copper wire winding resistance of compensation, 0 ℃, the RCu = 1; The Rs values can be calculated and determined according to the selected the type of thermocouple. This bridge in series in thermocouple measurement circuit, the thermocouple cold end RCu feeling the same temperature, the resistance under a certain temperature ( Usually take 0 ℃) Adjust the bridge balance, make the R1 = R2 = R3 = RCu. RCu when cold end temperature change with the temperature change, destroyed the bridge balance, to produce a voltage imbalance delta U, the voltage and thermoelectric potential superposition, together into the measuring instrument. Properly choose the value of Rs, but unbalanced voltage produced by the bridge delta U in a certain temperature range can basically compensation due to the cold end temperature of thermoelectric potential changes in value. So, when the cold end temperature have certain instrument still can give the right temperature value.