How to Measure the Safety Relay？

A safety relay consists of two parts: coil and contact. The coil resistance can be measured simply with Ohm, which is generally between tens and thousands. The coil power differs from AC current and DC current. In case of a short circuit, the coil may have burned out. Then disconnect the contacts and measure with Ohm band, the resistance value shall be infinitely-great. Connect the coil and measure, the circuit shall be shorted circuit. If the contact has a certain resistance, then it must be bad.

Measure the DC resistance of safety safety relay coil

Measurement method of a safety relay's DC resistance with a digital multiemter is similar to that with a pointer multimeter. According to the nominal DC resistance of safety relay, place the multimeter in an appropriate resistor and connect two test pens to the leading wire of the safety relay coil, then measure the resistance. Comparing the measurement result with the nominal resistance, if the error is within ±l0%, it's normal. If the resistance is obviously smaller, partial short-circuit fault exists in the coil; If the resistance is zero, the coil is short circuited; If the multiemter shows "1", the coil breaks.

Measure the actuation current

Actuation current is measured as the same as a pointer multimeter, namely placing the digital multiemter at 200mA DC band, then connecting it in series with the safety relay coil, a 5.1kΩ potentiometer and 200Ω resistor, connecting them with a 20V power supply.

Before measurement, turn the potentiometer to the maximum resistance first and then turn on the DC power supply, adjust the potentiometer slowly to reduce its resistance. When the safety relay attracts, the current shown on the multimeter shall be the attract current of the safety relay.

Measure the release current

After measuring the attract current, keep the circuit unchanged and measure the release current. When measuring, adjust the potentiometer slowly to increase its resistance while the safety relay is attracted, when the safety relay is about to release, the current shown on the multimeter shall be the release current.

Measure the contact resistance

Measure the resistance between two closed contacts with the 200Ω omh band of the multimeter. Generally, the resistance shall be near zero. If the multiemter shows "1", that means the two contacts are disconnected.

If the resistance is measured with buzzer band, the multiemter shall make a buzzer sound while displaying the resistance between two closed contacts. If the multiemter shows “1” and the buzzer doesn't make a sound, that means the two contacts are not connected.

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