Shanghai Chenzhu Instrument CO., LTD.
Shanghai Chenzhu Instrument CO., LTD.

What Main Parameters of Signal Surge Protector (SPD) Should be Noticed?

Jul 08 , 2021

1. Maximum continuous operating voltage (Uc): The maximum voltage of the signal circuit must be less than Uc

The maximum continuous operating voltage Uc is the maximum operating signal voltage, which is the maximum effective value of the signal voltage or DC voltage for the long-term operation of the surge protection device. This is also the maximum voltage between lines or between lines and ground under the condition of rated leakage current, which does not affect the normal operation of the circuit. For 24V DC power supply instruments, due to factors such as DC power supply voltage fluctuations and load changes, the maximum signal voltage value is: 30VDC~36VDC. Therefore, the maximum continuous operating voltage is Uc≥36V.

2. Rated working current IL: the maximum current of the loop is less than this value

3. Maximum signal current Ic

The maximum signal current is the maximum working signal current of the line where the industrial power surge protector is located.

For two-wire, three-wire, and four-wire 4mA~20mA signal meters (including HART communication signals), the maximum signal current value is: Ic≥150mA

For 24V DC power supply lines, such as solenoid valves, ultrasonic instruments, combustible gas detectors and other instruments, the value of the maximum signal current is: Ic≥600mA

4. Nominal discharge current In

The nominal discharge current In is the maximum surge current (8/20us) that the surge protection device by CHENZHU, a professional company in safety and automation system, normally passes through, which means that when the surge protection device passes the 8/20us standard experimental waveform current specified number of experiments (can withstand more than 15 times of induced lightning simulation T2 type (8/20us) waveform peak value), the maximum discharge current of the surge protection device is not damaged. For signal instruments, the nominal discharge current In is greater than 1kA to meet the general protection requirements, and specifications such as 5kA and 10kA can be selected.

5. Voltage protection level (UP)

The voltage protection level is the clamping voltage value of the surge protection device when it releases the surge current, which is also called the pass voltage or the limit voltage. This is the peak voltage at the output of the surge protection device when passing a 6kV/3kA 8/20us surge waveform generator or other specified experimental voltage and current.

For instruments with 24VDC working voltage, the voltage protection level of the surge protection device should be 60V. The limit voltage value of the applicable surge protection device should not be too high, generally about 2 to 2.5 times of the working voltage or signal voltage of the equipment to be protected. The voltage protection level should be less than the withstand voltage of the protected instrument such as a smart temperature transmitter.

6. Response time

The response time is the delay time from the moment when the standard experimental waveform voltage starts to act on the surge protection device to the moment when the surge protection device is actually turned on and discharged. The response time of the surge protection device should be ≤5ns.

7. Working frequency

The working frequency is the working frequency of the signal passing through the line connected to the surge protection device during normal operation. For instrument signals, including "smart" instruments, the operating frequency is below 20kHz, which is usually not counted.

8. Wire system

Choose the corresponding surge protection device according to the two-wire system, three-wire system or four-wire system. Thermocouples generally use two-wire systems, and thermal resistances generally use three-wire systems.

9. Is intrinsic safety required?

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