2-wire ac NC proximity sensor - PLCS.net

WrongWay · June 13th, 2011, 02:34 PM

These are not used very often I know. I do not have a PLC on this piece of equipemnt that I am attempting to install a monitoring/alarm circuit in. My intent is to use this prox to monitor for weld wire presence and to switch the load to a timer relay when no wire is detected. When the relay times out at 11 seconds it will latch a relay that sounds/lights an alarm condition that requires a key reset to unlatch. I installed the prox using a micro qd with #3 suppling load(120VAC) and #2 to the timer relay. Sometimes the prox doesn't light at all and other times after cycling power I have gotten a flash on/off from the red LED indicating a short circuit. Also, the micro qd cable I have the red/white to load and the red/black to the relay
How far off the track am I?

Lancie1 · June 13th, 2011, 02:44 PM

Is your "micro qd" some type of smart relay or electronic relay?

You have to be careful about what type and size of load you use with a prox switch. Not all prox switches will successfully switch all different loads (relays). DC relays can be difficult, as are some electronic relays.

WrongWay · June 13th, 2011, 03:57 PM

micro qd is a type of "quick disconnet" that has 3 terminals and 2 keyways to assure proper mating

WrongWay · June 13th, 2011, 04:20 PM

Thank you for the replies, both parts are AB.
The prox is a 871TM-B4C12-R3,switches up to 200ma. The timing relay is a 700-HRP42TA17. I grabbed the timer I had on the shelf and did not qualify it fully, it appears that it requires quite a load to energize it. As for the load to the prox, I put a 250ma AGC fuse inline before the prox.

keithkyll · June 13th, 2011, 04:47 PM

The prox needs a minimum load of 5 mA. There isn't a load spec on the timer datasheet. I suspect it might be small. Looked at similar Fuji timers from AD. They are only 10 VA. You should use a relay that draws at least 5 mA in between.

OkiePC · June 13th, 2011, 02:45 PM

If it's a two wire AC prox, then you should be able to wire it either way with the same results. I have seen some that also include a 3rd connection for ground.

If the prox is directly feeding the coil of a relay, then its indicator should always function unless it is damaged. Perhaps the prox was shorted or the load of the relay coil is too much for it?

Can you post a link to the part(s) you're using?

bkottaras · June 13th, 2011, 02:51 PM

Quote:

Originally Posted by OkiePC

If it's a two wire AC prox, then you should be able to wire it either way with the same results. I have seen some that also include a 3rd connection for ground.

If the prox is directly feeding the coil of a relay, then its indicator should always function unless it is damaged. Perhaps the prox was shorted or the load of the relay coil is too much for it?

Can you post a link to the part(s) you're using?

Ive seen both.
I agree with Paul.
Chances are that the load of the relay is too much for the prox. The prox is primarily used as a signal/feedback device and it is not capable of load switching. Check the prox specs.

keithkyll · June 13th, 2011, 02:52 PM

A 2 wire prox needs a good size load to power it's internal electronics. Check specs. I believe it's minimum 20 mA or so. Give it a load like an incandescent lamp.

Brijm · June 13th, 2011, 02:53 PM

Is it an electronic Timer? It may have too high of a resistance (minimum current to power the prox) Try putting a coil relay in between, or us a resistor to draw a few mA.

WrongWay · June 14th, 2011, 06:49 AM

I threw in a omron MY2 between the prox and timing relay. I was trying to minimalize the amount of components in the circuit by landing directly on the timer. Of course, no I can just use a NO prox. I guess what I learn here is that is a certain item is rarely used, its probably that there is a better, more mainstream way of doing it.
thanks again

tommy23t · June 14th, 2011, 11:20 AM

I would put a 10K ohm 2W resistor across the coil of the timer. AC switches need a minimum load to stay "on", this is common when using solid state timers to turn on a load.
tommy23t

keithkyll · June 14th, 2011, 11:28 AM

That's a common value, good for most applications. The problem is it will run a little hot.
For this application, 22K will give us a little over 5 mA, enough to meet the prox spec. Watts drops down to .6 Watts.

WrongWay · June 14th, 2011, 03:39 PM

I was able to test this today with no problems making the latch. The prox energizes the coil on a omron MY2 relay which closes a circuit to the timer. I'm probably missing something, but isn't there plenty of amperage to power that coil?

keithkyll · June 14th, 2011, 03:42 PM

Coil draws 9.2 mA at 120V. Well within your range of 5-250 mA for the prox.

June 13th, 2011, 02:34 PM	#1
WrongWay Member Join Date: May 2011 Location: Sturgis,Mi Posts: 31	2-wire ac NC proximity sensor These are not used very often I know. I do not have a PLC on this piece of equipemnt that I am attempting to install a monitoring/alarm circuit in. My intent is to use this prox to monitor for weld wire presence and to switch the load to a timer relay when no wire is detected. When the relay times out at 11 seconds it will latch a relay that sounds/lights an alarm condition that requires a key reset to unlatch. I installed the prox using a micro qd with #3 suppling load(120VAC) and #2 to the timer relay. Sometimes the prox doesn't light at all and other times after cycling power I have gotten a flash on/off from the red LED indicating a short circuit. Also, the micro qd cable I have the red/white to load and the red/black to the relay How far off the track am I? __________________ John In the land of plenty, conservation is a foreign word.

June 13th, 2011, 04:20 PM	#4
WrongWay Member Join Date: May 2011 Location: Sturgis,Mi Posts: 31	Thank you for the replies, both parts are AB. The prox is a 871TM-B4C12-R3,switches up to 200ma. The timing relay is a 700-HRP42TA17. I grabbed the timer I had on the shelf and did not qualify it fully, it appears that it requires quite a load to energize it. As for the load to the prox, I put a 250ma AGC fuse inline before the prox. __________________ John In the land of plenty, conservation is a foreign word.

June 13th, 2011, 02:45 PM	#6
OkiePC Lifetime Supporting Member Join Date: Mar 2005 Location: ENE of Nowhere Oklahoma Posts: 7,514	If it's a two wire AC prox, then you should be able to wire it either way with the same results. I have seen some that also include a 3rd connection for ground. If the prox is directly feeding the coil of a relay, then its indicator should always function unless it is damaged. Perhaps the prox was shorted or the load of the relay coil is too much for it? Can you post a link to the part(s) you're using? __________________ It's not all the variables I am most concerned with, it's the undiscovered constants. "You can lead a horse to water but if he's got his head up his as$ he may die of thirst anyway."

June 13th, 2011, 02:53 PM	#9
Brijm Lifetime Supporting Member Join Date: May 2006 Location: St. Marys, PA Posts: 580	Is it an electronic Timer? It may have too high of a resistance (minimum current to power the prox) Try putting a coil relay in between, or us a resistor to draw a few mA. __________________ Brian

June 14th, 2011, 06:49 AM	#10
WrongWay Member Join Date: May 2011 Location: Sturgis,Mi Posts: 31	I threw in a omron MY2 between the prox and timing relay. I was trying to minimalize the amount of components in the circuit by landing directly on the timer. Of course, no I can just use a NO prox. I guess what I learn here is that is a certain item is rarely used, its probably that there is a better, more mainstream way of doing it. thanks again __________________ John In the land of plenty, conservation is a foreign word.



This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
*Try our online PLC Simulator- FREE. Click here now to try it.* ---------->>>>>Get FREE PLC Programming Tips

June 13th, 2011, 02:44 PM	#2
Lancie1 Lifetime Supporting Member + Moderator Join Date: Jul 2003 Location: Alabama Posts: 7,263	Is your "micro qd" some type of smart relay or electronic relay? You have to be careful about what type and size of load you use with a prox switch. Not all prox switches will successfully switch all different loads (relays). DC relays can be difficult, as are some electronic relays. Last edited by Lancie1; June 13th, 2011 at 02:50 PM.

June 13th, 2011, 03:57 PM	#3
WrongWay Member Join Date: May 2011 Location: Sturgis,Mi Posts: 31	micro qd is a type of "quick disconnet" that has 3 terminals and 2 keyways to assure proper mating __________________ John In the land of plenty, conservation is a foreign word.

June 13th, 2011, 04:47 PM	#5
keithkyll Member Join Date: Jul 2005 Location: Lucas, TX Posts: 1,150	The prox needs a minimum load of 5 mA. There isn't a load spec on the timer datasheet. I suspect it might be small. Looked at similar Fuji timers from AD. They are only 10 VA. You should use a relay that draws at least 5 mA in between.

June 13th, 2011, 02:52 PM	#8
keithkyll Member Join Date: Jul 2005 Location: Lucas, TX Posts: 1,150	A 2 wire prox needs a good size load to power it's internal electronics. Check specs. I believe it's minimum 20 mA or so. Give it a load like an incandescent lamp.

June 14th, 2011, 11:20 AM	#11
tommy23t Member Join Date: Nov 2003 Location: New Jersey Posts: 134	I would put a 10K ohm 2W resistor across the coil of the timer. AC switches need a minimum load to stay "on", this is common when using solid state timers to turn on a load. tommy23t

June 14th, 2011, 11:28 AM	#12
keithkyll Member Join Date: Jul 2005 Location: Lucas, TX Posts: 1,150	That's a common value, good for most applications. The problem is it will run a little hot. For this application, 22K will give us a little over 5 mA, enough to meet the prox spec. Watts drops down to .6 Watts.

June 14th, 2011, 03:39 PM	#13
WrongWay Member Join Date: May 2011 Location: Sturgis,Mi Posts: 31	I was able to test this today with no problems making the latch. The prox energizes the coil on a omron MY2 relay which closes a circuit to the timer. I'm probably missing something, but isn't there plenty of amperage to power that coil? __________________ John In the land of plenty, conservation is a foreign word.

June 14th, 2011, 03:42 PM	#14
keithkyll Member Join Date: Jul 2005 Location: Lucas, TX Posts: 1,150	Coil draws 9.2 mA at 120V. Well within your range of 5-250 mA for the prox.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Hybrid Mode Switch to Threaded Mode

Similar Topics
Thread	Thread Starter	Forum	Replies	Last Post
4 wire proximity sensor to plc input	jeii	LIVE PLC Questions And Answers	9	March 14th, 2011 02:22 AM
AC proximity sensor	rguimond	LIVE PLC Questions And Answers	2	February 13th, 2011 08:37 PM
Inductive proximity sensor interfacing	xilog	LIVE PLC Questions And Answers	16	March 22nd, 2010 10:06 PM
How to connect AC sensor and motor to PLC	Zhen	LIVE PLC Questions And Answers	5	April 10th, 2009 06:47 AM
proximity sensor on sugar mill	labingtone	LIVE PLC Questions And Answers	6	January 17th, 2003 08:14 PM