1, zinc oxide pressure sensor application principle
The pressure sensitive resistor is used in parallel with the protected electrical equipment or components. When a lightning overvoltage or transient operation over voltage Vs occurs in the circuit, the pressure sensor and the protected device and the components are simultaneously with VS. Since the pressure sensitive resistor is very fast, it rapidly in the nanosecond time Excellent nonlinear conductive properties (see Figure 3 in the wearing area), at which time the voltage of the voltage resistor is rapidly decreased, far less than VS, so that the protected device and the actual voltage actually underde are much lower than over. Voltage VS, so that the equipment and components are from overvoltage impact.
2, parameter selection of zinc oxide pressure sensor
The voltage V1 mA under the specified current of the pressure-sensitive resistor is selected according to the protected power supply voltage. General selection principle is:
For DC loops: V1MA ≥ 2.0VDC
For AC loops: V1MA ≥ 2.2V Valid value
If the electrical device is low, the amount of surge energy is relatively large, the pressure sensitive resistor having a lower pressure sensitive voltage V1ma and a large slide diameter; if Vo is higher, the pressure sensitive voltage V1ma can be selected. Higher pressure sensitive resistors, such as protecting electrical equipment, and extending pressure sensitive resistance life.
3, method of use of zinc oxide pressure sensor
The pressure sensor is a non-polar overvoltage protection element, both communication or DC circuits, simply simultaneously reaching the pressure sensor and the protected electrical device or components (as shown in Figure 4) )
When the voltage amplitude is higher than the voltage under the specified current, the excessive power value is less than the maximum peak current of the pressure sensitive resistor (if the no pressure sensitive resistor is sufficient to make the device components destroy), the varistor is in the breakdown area. The overvoltage is constantly restricted on a very low amplitude. At this time, by the active resistor is not large (100A / cm2), it is not sufficient to degrade the pressure sensor; when an overvoltage When the value is very high, the pressure sensitive restriction limits the overvoltage to a lower level (less than the pressure level of the device), and the impact current of the device is very large, so that the pressure-sensitive resistor performance is deteriorated soon, At this time, the current through the fuse is very large, the fuse is disconnected, so that the electrical equipment, components are protected from overvoltage impact, and can also avoid due to the deterioration of the pressure sensor caused line LN, L-PE. Short-circuit (recommended fuse specifications are shown in Table 1).
In the overvoltage protection of the circuit, the pressure sensor is normalized in the pre-contained area and breakdown area of Figure 3, theoretically. However, since the pressure sensor is to withstand the power supply voltage, the temporary overvoltage of the circuit, the ultravoluential overvoltage random, and the energy storage element is released, and therefore, the pressure sensor will be damaged, its life Different from the excessive amplitude and energy subjected to the circuit.