Reasonable selection of thermocouple wiring way more advantageous for its use

Thermocouple in use at ordinary times, usually paid little attention to the connection in the circuit problem, at least most unprofessional people won't think of this problem, we have three cheong instrument technical personnel to explain in detail for everybody in this specific circuit wiring.

thermocouple under normal circumstances is usually have 2 line, line 3, 4 line connection!

2 wire measurement, the measurement of the corresponding temperature resistance is the resistance of the thermocouple wire, three wire system circuit by changing the measurement method of the circuit to eliminate the influence of wire resistance, it is pure thermocouple measurement of resistance, especially when the line is longer than the effect of this. Sensor resistance value changes and connection wire resistance of sensor output value, because of the additional error caused by wire resistance make the actual measured values on the high side, used for measuring accuracy is not high, and the length of the wire shoulds not be too long.

3 wire measurement requirements of three wire cross-sectional area and length are the same, the circuit of platinum resistance measurement is generally unbalanced bridge, platinum resistance as a bridge arm resistance of bridge, will lead a received the power supply end of the bridge, the two remaining root respectively received a platinum resistance of bridge arm and the adjacent bridge arm, when the balance bridge road, through calculation, the Rt = R1R3 / R2 + R1r/R2 - R, when R1 = R2, the wire resistance change on measurement result does not have any effect, thus to eliminate the measurement error brought about by the conductor line resistance, but must be congruent arm bridge, otherwise can't completely eliminate the influence of wire resistance, but the analysis can be seen, using three wire system will greatly reduce the wire resistance, the additional error of industry generally adopted three wire connection.

4 wire system to measure the resistance value is very small, the resistance of the test line may introduce significant error, four-wire measurement with two additional test line to provide constant current, and the other two unknown resistance of the voltage drop is measured test line, under the condition of the voltmeter input impedance is high enough, current flow is almost no voltage meter, so you can accurately measure the unknown resistance pressure drop of the calculated resistance value.

thermocouple measurement system, however, the conductor also have a similar heat - thermocouple measuring element Coupling effect, the use of three wire connection is to eliminate the measuring error caused by the wire resistance change.

use two lines to connect, is in commonly accepted ( Tolerance) Measuring error caused by the wire resistance change, or wire resistance is very small, Cross section is very big or very short distance) That case.

the first to use three lines connect method to measuring equipment and the use of second-line compared method measuring the equipment, three line method after the temperature of the measured data, compared with the actual temperature data have the characteristics of more precisely. From that on the one hand, is sure a lot of measuring temperature work, should be used when I was in the third line method.

the three wire system is to eliminate the measuring error caused by the connection wire resistance. This is because the measuring circuit of thermocouple is usually unbalanced bridge. Thermocouple as a bridge bridge arm resistance, its connection wire ( From the thermocouple is controlled by the) This part also become a part of the bridge arm resistance, resistance is unknown and change with environment temperature, cause measurement error. Using three wire system, will lead a received the power supply end of the bridge, the remaining two received thermocouple respectively the bridge arm and the adjacent bridge arm, this eliminates the wire line resistance measurement error.

second while using four wire connect method to measuring devices, measurement data is more accurate, but using three lines connect method to measuring equipment can be used in long narrow measuring range or wires environment, and even lead long, also won't appear the measured temperature value because of the characteristics of long wires numerical change.

through the above introduction, the circuit of thermocouple wiring should also be aware of, to thermocouple when using more safe and more long, everyone in the connection must be the right choice when its way!