Can you parallel thermocouples

The two thermocouple wires must be welded together from one side to form a junction. Inconsistent readings can be generated from loose junctions such as twisted wire joints. For example, Type K is composed of a positive Chromel wire and a negative Alumel wire. A thermocouple is troublesome for any voltage-measuring instrument with high input impedance because the lack of a complete circuit on the input enables electrical noise from surrounding sources power lines, electric motors, variable-frequency motors to be detected by the instrument and falsely interpreted as wildly variable temperature.

Thus, when a single thermocouple is connected to two devices, the reaction of the thermocouple to burn-out conditions should also be deemed. Presuming the device pulls high input voltage in burnout condition, the other device will not be able to recognize the burnout condition.

Making Parallel Thermocouple Measurements. What are parallel thermocouple measurements? Follow Us. Your email is never published nor shared. Search Applications and News. New, Free. Net Classes and Example Programs ».

Making Parallel Thermocouple Measurements. Posted by Daqhelper ; Published March 15, As a result, thermocouples require accurate and sensitive measuring devices and cannot be used for temperature changes of less than about 0.

Traditionally, expensive voltage balancing potentiometers were used to measure emf. Today, a high quality digital voltmeter is sufficient [3]. The National Institute of Standards and Technology NIST has developed standard calibration curves for determining temperature based on the measured emf voltage. These data represent the output emf of thermocouples when an ice cold junction is used, and are incorporated in the memory of most DAQ systems. Obviously, the higher the order of the polynomial function, the higher the accuracy of temperature reading.

The polynomial function should only be used inside the temperature range of the thermocouple type and should not be extrapolated. To save computational time, a lower order polynomial fit can be used for a smaller temperature range. Thermocouple wires come in variety of sizes.

Usually, the higher the temperature, the heavier should be the wire. As the size increases, however, the time response to temperature change increases. Therefore, some compromise between response and life may be required. Thermocouples can be connected electrically in series or in parallel.

When connected in series, the combination is usually called a thermopile, whereas there is no particular name for thermocouples connected in parallel.