Difference between thermocouple and RTD

I. Nature of the signal

RTD itself is resistance, temperature changes, so that the resistance to produce positive or negative resistance changes; and thermocouple is to produce changes in the induced voltage, he changed with the temperature. Although they are contact temperature measuring instruments, but their temperature measurement range is different, thermocouple used in higher temperature environment, such as platinum rhodium 30 - platinum rhodium 6 (B type) measurement range of 300 degrees ~ ~ 1600 degrees, short-term can be measured 1800 degrees.

The S-type measures 20~~1300 (short-term 1600), the K-type measures 50~~1000 (short-term 1200), the XK-type measures 50~~600 (800), and the E-type measures 40~~800 (900). There are also J-type, T-type and so on. This type of instrument is generally used for higher temperatures above 500 degrees, low-temperature zone when the output thermal potential is very, when the potential is small, the anti-interference measures and the secondary table and the requirements are very high, otherwise the measurement is not allowed, and, in the lower temperature region, the cold end of the temperature changes and changes in the ambient temperature caused by the relative error appears to be very prominent, it is not easy to get the full compensation. At this point in the low temperature, the general use of RTD temperature measurement range of a 200 ~ ~ 500, and even lower temperatures can be measured (such as carbon resistance can be measured to the low temperature of about 1K).

Now normal use of platinum RTD Pt100, (also Pt50, 100 and 50 represents the resistance value of RTD at 0 degrees. In the old scale number with BA1,BA2 to indicate that BA1 at 0 degrees resistance value of 46 ohms, in the industry is also used in copper resistance, scale number for CU50 and CU100, but the temperature range is small, in a 50~~150, in some special occasions there are indium resistance, manganese resistance, etc.).

Ⅱ、On-the-spot judgment at work

Thermocouples have positive and negative poles, and compensation wires also have positive and negative poles. first ensure that the connection is made and the configuration is sure. In operation. Common short circuit, broken circuit, poor contact (with a multimeter can be judged) and deterioration (according to the surface color to identify).

Check, to make the thermocouple and the secondary table separate, with a tool to short the secondary table on the compensation line, the table indicates the room temperature and then short the thermocouple terminals, the table indicates the thermocouple is located in the ambient temperature (not, the compensation line is faulty), and then use the multimeter mv gear roughly estimated thermocouple thermal potential (such as normal, please check the process). RTD short circuit and disconnection with a multimeter can be judged, in operation, suspected short circuit, as long as the resistor end to remove a wire to see the display meter, such as to the maximum, RTD short circuit back to zero, wire short circuit, to ensure that the normal connection and configuration, the table value shows low or unstable, the protection of the tube possibility of water in the display of the maximum, RTD disconnection shows the minimum short-circuit.

Ⅲ、material wise

Thermal resistance is a metallic material with temperature-sensitive changes. Thermocouples are bimetallic materials, both two different metals, which produce a potential difference at the ends of two different wires due to changes in temperature.

Ⅳ、The two sensors detect different temperature ranges

Thermal resistance generally detects a temperature range of 0-150 degrees (negative temperatures can be detected, of course), and thermocouples can detect a temperature range of 0-1000 degrees (or even higher), so the former is a low-temperature detection, and the latter is a high-temperature detection.