Thermal resistance and display instrument wiring method
It is known from the thermal resistance temperature measurement principle that the change of the measured temperature is measured by the change of the resistance of the thermal resistance. Therefore, the change of the resistance of the wire connected to the thermal resistance will bring errors to the temperature measurement. Whether this influence needs to be eliminated is related to the application occasion, application requirements and accuracy requirements for temperature measurement, so there are a variety of wiring methods. However, the temperature measurement principle of two-wire, three-wire and four-wire thermal resistance is the same, but the wiring is different. The actual problem is whether the current loop and the voltage measurement loop are wired separately. But it should be emphasized that the three-wire and four-wire wiring method must be used in conjunction with the corresponding wire-based thermal resistance element to achieve true three-wire and four-wire wiring. The two-wire connection method of thermal resistance is mainly used for short-distance temperature measurement sites. The two-wire connection method does not consider the influence of the change of wire resistance, so its measurement accuracy is low and can only be used for temperature measurement requirements Not high occasions.
The three-wire connection method of thermal resistance is widely used in industrial production, mainly used for long-distance temperature measurement, which can reduce the influence of the change of the resistance value of the connecting wire on the value of the instrument. But in reality, most of the thermal resistance used in many factories, the thermal resistance element in the protection tube has only two leads, that is, the thermal resistance element is a two-wire system, although three connecting wires are used from the protection tube junction box to the display instrument, but this It can only be regarded as a two-wire thermal resistance wiring method, or a three-wire thermal resistance two-wire wiring method.
The four-wire wiring method is mainly used in laboratories to obtain high-precision measurement results. When used, it is mainly to apply a stable current to the thermal resistance, and then measure the voltage (potential) on the thermal resistance to improve the measurement accuracy and sensitivity. In the industrial production, there are four terminals: I+, I-, V+, V- for meters and board modules connected with thermal resistance. Among them, the I+ and I- terminals provide constant current to the thermal resistor, and V+ and V- are used to monitor the voltage change of the thermal resistor to obtain the temperature change. The wiring principle is shown in the figure. When the measuring instrument uses the principle of potential difference measurement, although the wire has resistance, the voltage drop on the wire through which the current flows is not within the measurement range. Although the wire connecting the measuring instrument also has resistance, no current flows, so four The resistance change of a wire has no effect on the measurement result, but the current of the constant current source is required to be stable.
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