using NAMUR switch in place of PNP prox?

[robbm]

i had planned on having a valve control unit that used 24VDC PNP proximity switches built into it to sense when the valve opens and closes (wired back to an AllenBradley 'sinking' PLC input card). our purchasing manager cannot get the control unit with a PNP switch in the timely fashion he wants and has asked me if we can use a 2wire NAMUR switch instead. do i need an isolator or anything special to make this work with my PLC input card? bytheway, this is going into a non-hazardous area.
thanks in advance.

 

[itsmoked]

Got a data sheet? <NAMUR>???

Keith Cress
kcress -

http://www.flaminsystems.com

 

[robbm]

no data sheet, but here's the order sheet for it. it says it's a non-amplified, does that mean a standard 24VDC supply will or will not work?

 

[Kiljoy]

That is not a replacement for a standard 24V PNP prox switch going to an AB input card. If your purchaser can't find a dime-a-donzen prox, then find a new purchaser. If the prox you are looking for is something special, let us know the specs and maybe we can suggest something.

 

[robbm]

the key is which of the switch types will work with a sinking-type AB input card. the order/spec sheet above for that valve control-top lets you select between a 3wire PNP prox or a 2wire NAMUR switch (among other types). we usually use the 3wire version for this control-top but it's got a longer delivery right now, so purchasing was wondering if we could use the NAMUR version instead (it's readily available from the control-top MFR), it's not a matter of just using another prox, it has to be selected from the list on that spec sheet (we dont have a choice in the brand of control-top we are using). the basic question is can a NAMUR prox be used the same as a 24VDC PNP prox?

 

[Kiljoy]

I had to do a little research on what a NAMUR switch it. I would say the answer is no. A NAMUR switch is current driven. An AB input card that would work with a PNP prox would be voltage driven. I would say that a NAMUR switch could be used with a 4-20mA analog input card, but not a discreet digital input card.

It may be possible to build a circuit that sends a digital signal to your card based on the output of the NAMUR sensor. What other configurations were readily available? Was it just the NAMUR?

 

[robbm]

Those were the only two options. I'm thinking it wouldn't work as well because I've seen applications with NAMUR switches in intrinsically safe areas and they were wired thru an ampliifer or IS barrier, so I told our people to stick with the 24V PNP.

 

[DYV1973]

Namur requires 8.3V, so you need a converter. P&F switch amplifiers can convert the Namur into PNP/NPN active or passive. We have used them a lot succesfully.