Thermocouples are used to measure furnace temperature. The indexing number of the thermocouple is mainly selected according to the measured target temperature. Of course, it is also necessary to consider whether the measured atmosphere is reducing or oxidizing; if armored thermocouples are used, there is not much consideration for the effect of redox atmosphere on thermocouples. The impact of life and measurement accuracy.
Most furnaces need to be connected to more than one thermocouple, at least one of which is used for temperature control and the other for recording. Because our processing process needs to be traceable, when encountering a relatively large furnace body (a length of more than 5 meters), it must be divided into several temperature zones for independent measurement and control, such as upper, middle and lower partitions. More stringent furnace bodies should be tested for furnace temperature uniformity on a regular basis. That is, multiple thermocouples (or other sensors) are evenly arranged in the working area to simulate the normal use process and load to test whether the temperature of the furnace body is uniform over time and other factors. That is, whether the temperature measurement point of the temperature control thermocouple can represent the true temperature of the furnace temperature, and more than one measure each value.
The main applications of thermocouples are measurement and calibration. Moreover, the thermocouple is a primary instrument, which converts temperature into electric potential, and this weak electric potential is sent to the secondary instrument for processing, display or printing. The secondary instrument is divided into analog type and digital type. It's basically all numbers now.
A thermocouple cold junction temperature compensation circuit, the circuit includes a voltage temperature sensor TMP35 and a K-type thermocouple. The working principle of the thermocouple is based on the temperature difference between the hot end and the cold end to generate a potential difference. Since the temperature of the cold junction is often not 0°C during actual measurement, temperature compensation should be performed on the thermocouple. The thermocouple temperature compensation formula is as follows:
E(t,0)=E(t,t0)+E(t0,0)
Among them, E(t0,0) is the actual measured electromotive force, t represents the temperature of the hot end, t0 represents the temperature of the cold end, and 0 represents 0°C. In the field temperature measurement, since the temperature of the cold junction of the thermocouple is generally not 0°C, but changes within a certain range, the measured thermoelectric potential is E(t, t0). If you want to measure the thermoelectric potential E(t,0) corresponding to the real measured temperature, you must compensate the compensation potential E(t0,0) required for the cold junction to not be 0°C, and the compensation potential varies with the temperature of the cold junction The characteristics of the change must be consistent with the thermoelectric characteristics of the thermocouple, so that the best compensation effect can be obtained. It is a circuit diagram of thermocouple cold junction temperature compensation. The temperature sensor TMP35 completes the temperature compensation work well. The voltage output by the TMP35 is first divided by the resistance, and then amplified by the amplifier, which is the E (t0, O) corresponding to the K-type thermocouple.
