How to convert thermal resistance signal to rough temperature using multimeter
Both commonly used pointer multimeters and digital multimeters can roughly estimate the approximate temperature range of a thermal resistor.
The commonly used thermal resistors include (P platinum resistors) Pt100, Pt1000, and (C copper resistors) Cu50, Cu100.
The measurement range of Pt100 thermal resistance is -200~850 ℃, with a minimum range of 50 ℃, an absolute error of ± 0.2 ℃, and a basic error of ± 0.1%. The measurement range of Pt1000 platinum resistor is only -200~250 ℃, and other parameters are exactly the same as Pt100.
The measurement range of Cu50 and Cu100 is -50~150 ℃, with a minimum range of 50 ℃, an absolute error of ± 0.4 ℃, and a basic error of ± 0.1%.
Let's talk about PT100 thermistor below.
Pt100 is just an acquisition and detection component, which must be equipped with an auxiliary 5V~24V DC single power supply during operation. Using the Wheatstone bridge principle, the electrical signal that varies linearly is sent to the integrated operational amplifier block or isolated transmitter, and processed by a single-chip chip to truly reflect the temperature value of the measured object. The temperature controller issues corresponding commands to control the temperature of the controlled object.
The commonly used PT100 thermistor is divided into two wire, three wire, and four wire systems. From its scale, it can be seen that its measurement range is relatively large, ranging from -200 ℃ to+600 ℃.
The so-called PT100 actually refers to its resistance value of 100 Ω (ohms) at standard 0 ℃. And as the temperature drops below zero, its resistance value gradually decreases. The resistance value at -200 ℃ is about 18.5 Ω. And when the temperature rises from 0 ℃, its resistance value increases. For example, when the temperature rises by 50 ℃, its resistance value is about 119 Ω (ohms). At 100 ℃, its resistance value is about 138 Ω (ohms). At 200 ℃, its resistance is about 176 Ω (ohms), and at 600 ℃, its resistance is about 313 Ω (ohms).
As mentioned above, Cu50 thermistor can be derived, where 50 Ω refers to its resistance value at 0 ℃. When it is at -50 ℃, its resistance value will decrease from 50 Ω to 39.2 Ω. When it rises from 0 ℃ to 50 ℃, its resistance value will increase to 60.7 Ω, and so on. At 150 ℃, its resistance value will rise to 82.13 Ω.
From the above, it can be seen that both PT100 thermistor and Cu50 thermistor have a large dynamic range and linear resistance law. When they are assigned to many types of temperature controllers to achieve temperature acquisition and control, the effect is good. Therefore, it is widely used in high-precision temperature equipment such as medical treatment, motor manufacturing, cold storage, industrial control, temperature calculation, bridge resistance calculation, etc., with a wide range of applications.
For the convenience of everyone using a multimeter to check the commonly used two types of thermal resistors, Pt100 and Cu50, the following is a scale table for producing these two types of thermal resistors for comparison and testing.
