Using x90 safety input for safety bumper

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1

Hello

I have an X90CP154 with SafeLogic and would like to connect a safety bumper. The bumper has a resistance of 10kΩ in the idle state and closes the contact when pressed.

I am now unsure how to evaluate this safely with the X90. According to the manual, the safety inputs can be used in the following configurations:

  1. Current-sourcing digital input

  2. Voltage input

  3. Current input

  4. Resistance and temperature input, although only in dual-channel configuration

My analysis so far:

  1. This would work, but there would be no wire-break detection, so that option is out.

  2. In the wiring example, a voltage source is shown. Does an external voltage divider count as a voltage source? And could I then safely measure the voltage and evaluate in the safety logic whether there is a wire break, idle state, or activation?

  3. In this case, a current source is shown. I could measure the current if I connect the bumper to a voltage supply and to the input:

  • no current → wire break

  • small current → idle state

  • high current → activated

  1. For the resistance input, the manual states that this is only safe in dual-channel configuration, so I assume this option is also not suitable?

Maybe someone has experience with this and knows how this is usually implemented. Thanks in advance for any help!

Best regards, Robert

2

Hello,

I do not have expirience with this and I can not give any safety recomendations but i like to share my thoughts on this.

I think the supplier of this Pumper has the best understanding in how he has designed the electrical cirquite and how he had intend to make this safety readable and relyable.

In my opinion an Voltage devider is a valid voltage source, because the Voltage source is the supplying voltage of the devider. The devider only modifies the hight of the voltage.

A Voltage devider with a 15kOhm and a 5 kOhm would give you a very good readable state, as you already descriped.

Bumper 0 Ohms → 0V → Bumper pressed
Bumper 10kOhms → half Supply Voltage → Pumper ok
Bumper wire Break → 1/4 Supply Voltage → Wire Break
24V connection on Cable 1 → full Supply Voltage → 24V Connect
24V connection on Cable 2 → short circutie on supply → 0V interpreted as bumper pressed?

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I think it could be possible to make the divider more complex with an additional resistor on the 0V Line. I think the requirements of possible to detect failtures should come out of a risk analysis.

Greetings
Michael

3

Thank you very much Michael. We will do it exactly like this and see what the risk analysis reveals.
Best regards, Robert