	Proximity Sensors

Hints on Correct Use/General Notes

Hints on Correct Use

Cable disconnection alarm output(ES-32DC)

Correct use of the cable disconnect alarm

The alarm output will be triggered when the sensor head cable becomes disconnected or if it is wired incorrectly, notifying the operator of a malfunction.


*	It is recommended that the ES-32DC unit be connected to a self-holding circuit, otherwise alarm output may be intermittently output in the early stages of wire breakage.

Ensuring horizontal positioning accuracy

Diagram showing how to ensure horizontal accuracy

For the ES Series, repeatability data is provided only for the direction perpendicular to the detecting surface of the sensor head. If the same level of accuracy is required horizontally, adjust the sensitivity adjustment trimmer to achieve the detection conditions as shown here.

2-wire proximity sensors

Residual voltage

The impedance of the 2-wire-type proximity sensor's circuit, when output is ON, produces a voltage which is the difference of the voltage across the 2 wires connected to it (V1, 0 V). This means that the voltage across the load (V2) is equal to the supply voltage minus V1 (V2 = Vs - V1). Make sure that V2 is greater than the operating voltage of the load. (Refer to the Characteristics chart "Residual voltage".)

Circuit diagram for a two wire proximity sensor

Effects of leakage current

With a 2-wire proximity sensor, a small amount of current flows (leakage current) to keep the circuit operating even when the sensor is turned OFF. (Refer to graph "Leakage current characteristics".)
Because of this current, a low voltage remains on the load, sometimes preventing the load from properly resetting. Before operation, check that the residual voltage is lower than the reset voltage of the load.

When the load current is low

When the load current is less than 5 mA, connect a bleeder resistor to give the sensor 5 mA or more load current. Make sure the residual voltage is less than the reset voltage of the load.

Circuit diagram for a low load load current

General Notes

Interference

When 2 or more proximity sensors of the same model are closely installed side-by-side, the high-frequency magnetic fields of one sensor may disturb the other sensor's operation. This phenomenon is called interference.

Eliminating interference

	Use a proximity sensor that can be switched to an alternate frequency (EM Series).
	Use interference suppression function. --- ES-M1, M2
	Provide the proximity sensor with an interference prevention adaptor.(ES Series)
	Allow sufficient distance between sensors to prevent interference. (For further information, refer to the section "Hints on correct use" for each model.)
	Use sencors of different models. (Contact KEYENCE for details.)

Surrounding metal

When embedding a proximity sensor in a metal base, provide the distances specified for each model to minimize interference from the surrounding metal. For details, refer to the section "Hints on correct use" for each model.

Miscellaneous

	When using a commercially available switching regulator, ground its chassis grounding and earth grounding terminals.
	Isolate sensor wiring from power lines and highvoltage lines; otherwise, the sensor may malfunction due to noise interference.
	Loads (lamps, motors, etc.) having a rush current 10 times greater than the rated current will damage or break the output circuit. For such loads, use external relays with a sufficient rated capacity. Also, to protect sensors from surge due to the counter-electromotive force of a relay coil, use relays with a surge-absorber.

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