According to the instructions from six aspects of thermocouple preventive measures and matters needing attention

From six aspects that preventive measures and matters needing attention of using thermocouple

most measurement problems and errors and thermocouple due to lack of understanding of thermocouple work. Listed below are some questions need to be aware of common and myth.

many measurement error connection problem is caused by accidental thermocouple. Remember that any connection of different metal will cause the knot. If you need to increase the length of the thermocouple wire, you must use a thermocouple wire type (right Such as K type thermocouple K type) 。 Use other types of thermocouple wires to a. Any use of the connector must be in the right and correct polarity must abide by the thermocouple materials.

the lead resistance in order to reduce the heat and to improve response time, thermocouple by the thin lines ( In the case of platinum cost is also a factor) 。 This leads to the thermocouple with high resistance, can make it is sensitive to noise, can also lead to error of the input impedance of a measuring instrument. A typical exposed junction thermocouple (32 AWG wire Diameter of 0. 25 mm) Will be about 15 ohms resistor/m. Pico TC- There are two meters & Omega 08 instrument; The input impedance, so there will be less than 12 meters of cable 0. 01% error. If the conductor is fine and long cable thermocouple is necessary, it is worth keeping thermocouple wire short, and then with the thermocouple wire ( This is thicker, so has low resistance), Running between thermocouple and measuring instrument. It is always before using measuring thermocouple resistance of your good preventive measures. Calibration downgrade

this is not change the makeup effect of thermocouple wire. Usually is the cause of atmospheric particles to the metal in the operating temperature extremes. Another reason is from thermal diffusion to thermocouple wire and chemical impurities. If at high temperature operation, check the insulation of the probe.

noise from the thermocouple output signal is very small, so it is easy to happen electrical noise pickup. Most of the measuring instruments ( Such as the TC - 08 instrument) To refuse any common mode noise, The line is the same signal) , noise can help ensure that together through the twisted cable wire to the same to minimize noise. In addition, the TC - 08 instrument using an integrated analog to digital converter help any remaining noise on average. If in a very noisy environment, work ( As in the large motor) Is considering adopting shielded cable is worth promoting. If the suspect is pick up noise, first turn off all suspicious devices to see the change of reading.

common-mode voltage while thermocouple signal is very small, big often exist in the input voltage to the measuring instrument. The voltage may be sensor ( A problem, the test and the temperature of the transformer windings) Or & other Grounding & throughout; The connection. A junction of a typical example of grounding is a thermocouple measuring temperature of hot water pipe insulation. If you have any bad grounding connection, a few volts may exist between tube and the measuring instrument to earth. These signals are then normal mode ( The thermocouple wire) So most of the instruments in no problem as long as it's not too big. For example, the TC - 08 instrument has a common-mode input range is 4 V to 4 V– If the common mode voltage is greater than this, will lead to a measurement error. Can minimize common-mode voltage, use the same wiring to prevent noise, and USES the thermocouple insulation.

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all thermocouples are quality. Heating quality needs energy, it will affect your measuring temperature. Such as measure fluid temperature in test tubes, there are two potential problems. First, the heat will travel to the thermocouple wire and dissipate into the atmosphere, reduce the wire around the liquid temperature. If the thermocouple is not fully soaked in the liquid will appear similar problem. Due to the cold air temperature on the wire, heat transfer can lead to thermocouple is in different temperature of the liquid itself. In the above example, the use of fine wire thermocouples may be helpful, because it can lead to a steep gradient along the thermocouple wire junction between the liquid and air temperature. If use thread thermocouple, it is the resistance of the conductor must be considered. A thin line connected to the thicker with the use of the thermocouple wire thermocouple tend to offer the best compromise.