What is the material constant of a thermistor?

The chip of a thermistor (a semiconductor ceramic) is sintered at high temperatures to form a material with a certain resistivity, and there is only one b value for each formulation and sintering temperature, which is called the material constant.

The b-value can be calculated by measuring the resistance values at 25 degrees Celsius and 50 degrees Celsius (or 85 degrees Celsius). The B value is positively correlated with the temperature coefficient of the product resistance, which means that the higher the B value, the greater the temperature coefficient of resistance.

The temperature coefficient is the rate of change in the resistance value for every 1 degree increase in temperature. The b value can be converted to the temperature coefficient of resistance using the following formula:

The temperature coefficient of resistance b is t2 (t is the absolute temperature value of the point to be converted).

A thermistor with a positive temperature coefficient increases its resistance as the temperature increases. Conversely, it is a thermistor with a negative temperature coefficient.

The former is a slow type, and the temperature coefficient of resistance at room temperature is between +; The latter is a switching type, and in a small temperature range, the resistance value increases by several orders of magnitude, and the temperature coefficient of resistance can reach +

First, the working principle is different.

1. Thermistor: When the circuit is working normally, the thermistor temperature is close to room temperature, and the resistance is very small. The series connection does not impede the passage of current in the circuit.

When the circuit is overcurrent due to a fault, the temperature of the thermistor increases due to the increase in heating power. When the temperature exceeds the switching temperature, the resistance increases dramatically and the current in the loop rapidly decreases to a safe value.

2. Metal RTD: The temperature measurement principle of RTD is based on the characteristics of the resistance value of the conductor or semiconductor changing with temperature, measuring the temperature and temperature-related parameters. Thermal resistance is mostly made of pure metal materials.

Currently, platinum and copper are the most widely used materials. Now, nickel, manganese, and rhodium have been used to make RTDs. RTDs typically require a resistance signal to be transmitted via a wire to a computer control or other secondary instrument.

Second, the characteristics are different.

1. Thermistor:

1) The temperature coefficient of resistance is 10-100 times larger than that of metal, and the temperature change of 10-6C can be detected.

2) The working temperature range is wide, the normal temperature device is suitable for -55 315 degrees Celsius, the high temperature device is suitable for more than 315 degrees Celsius (currently up to 2000 degrees Celsius), and the low temperature device is suitable for -273 55 degrees Celsius.

3) Small enough to measure the temperature of voids, cavities, and blood vessels that other thermometers cannot.

4) Easy to use, the resistance value can be arbitrarily selected;

5) It is easy to process into complex shapes and can be mass-produced;

6) Good stability and strong overload capacity.

2. Metal RTD:

1) Pressure spring type temperature sensor, good vibration resistance;

2) High accuracy of temperature measurement;

3) High mechanical strength, high temperature and high pressure resistance;

4) Imported thin film resistor, stable and reliable performance.

1.Metal resistance (e.g., platinum) rises with temperature;

2.Thermistors (e.g., manganese oxide) decrease as temperature rises;

3.Compared with thermistors, metal thermal resistance has good chemical stability and a large measuring range, but the sensitivity is poor.