Limit switches

[adamscb]

Forum,

I need some help/info on ordering some limit switches. What I'm looking for is a limit switch that when closed has a 24v DC output, that we can wire into our DCS system as a digital input for system indication purposes. Obviously this limit switch needs some sort of power supply, so I'm thinking 120v.

All of the limit switches I'm finding are just that - switches - and have no voltage output. Has anyone found limit switches that have a voltage output? Thanks

 

[mgookin]

A switch has a rating. It's output is only whatever the input is.

To source the switch you need to know the load.

As an EIT are you working under someone?

 

[infinity]

Forum,

I need some help/info on ordering some limit switches. What I'm looking for is a limit switch that when closed has a 24v DC output, that we can wire into our DCS system as a digital input for system indication purposes. Obviously this limit switch needs some sort of power supply, so I'm thinking 120v.

All of the limit switches I'm finding are just that - switches - and have no voltage output. Has anyone found limit switches that have a voltage output? Thanks

So you're thinking that you would supply this switch with 120 VAC and when closes it would output 24VDC? If there is no such animal you might need to supply a 120VAC-24VDC voltage transformer and then run one side of the 24 VDC through the switch contact.

 

[iwire]

Forum,

I need some help/info on ordering some limit switches. What I'm looking for is a limit switch that when closed has a 24v DC output, that we can wire into our DCS system as a digital input for system indication purposes. Obviously this limit switch needs some sort of power supply, so I'm thinking 120v.

All of the limit switches I'm finding are just that - switches - and have no voltage output. Has anyone found limit switches that have a voltage output? Thanks

I have never seen such a switch, I can't say one does not exist but finding it could be hard.

If it was me I would first check if the DCS system is capable of supplying the 24 VDC it needs to see at the input. In my experience many will have this ability.

If not just purchase a small DC supply for it.

There are many types available. https://power.sager.com/mdr-10-24-2...=power-brand&gclid=CJ6F_7HlwdECFRKBswodDzIPLQ

 

[adamscb]

It sounds like there's no such thing as a limit switch that can output it's own voltage. So what I will have to do in my mind is to wire an output from the DCS system (24v), to the limit switch, and then when the limit switch closes that sends the 24v to an input into the DCS system. That's the easiest way I see in doing it.

And no, my mentor left the company 6 months into me being hired. I inherited all of his projects (one being 3+ million $$) and I'm trying to wrap them up.

 

[iwire]

So what I will have to do in my mind is to wire an output from the DCS system (24v), to the limit switch, and then when the limit switch closes that sends the 24v to an input into the DCS system. That's the easiest way I see in doing it.

That is the way I always see almost all the time. Sometimes an external power supply,

 

[Jraef]

Unless perhaps the inputs are each individually opto-isolated, it's entirely possible that your DCS people would have a CONNIPTION FIT if you brought in a foreign source of 24VDC. Doing so can carry noise along with it that can cause all sorts of other problems. Using the same source of 24VDC as all of the other inputs use is the preferred method. Alternatively, you can run the limit switch circuit at any voltage you like, then use an "interposing relay" at the DCS or its mashalling cabinet to isolate that signal and connect the 24VDC to the input.

 

[Ingenieur]

The dcs or plc typically supplies the switched voltage to dry contacts