one shot

Hello
Is it possible to make a one shot with regular mechanical relays?

May I ask what relay application would require this?

I have 4 tank with low level sensors that I want to sound an alarm when ever a tank goes down and reset the alarm with a push button. So I wanted to "or" all the 4 low level sensors to a nc push button to a self latching relay.

I am not sure that the term 'one shot' can be applied to mechanical relays, after all there is no scan of mechanical relays.

Perhaps what you actually want is a relay that will only stay on for x amount of time, that would be a timer relay then. I doubt if you will get a timer relay that could mimic the scan time of a PLC (maybe 5mS)

From your description given to Ken, I still can't visualise why you want a 'one shot', then again maybe my brain ain't working as good as it should do, I have had a long hard day getting my head around a S5 program written in STL with all the anotation in German.

Paul

I think you need something like this:



It will alarm from the time any of the sensors clses until the reset button is pressed. It will continue alarming if the operator releases the N.C. reset button while an alarm condition still exists. Need something differrent?

Years ago you could buy a two coil mechanical latching relay that would latch on if you energized the set coil momentarily and would stay on until you energized the reset coil momentarily.

The attached pdf file shows three level sensors that activate an alarm, by pusing the PB you can silence the alarm, even if the alarm is still active.

ready961 said:

Hello
Is it possible to make a one shot with regular mechanical relays?

Click to expand...

Yes, but you've got to know how much time you want your oneshot to stay closed for.

Basicly the oneshot is operated by a NC contact on a timer. Lets say that your control voltage is 110vac. Standard .3-3.0 sec KH 4pole timer. Your driving (input) signal would be connected to Pins 13 & 9. The oneshot output would be connected to Pin 1. (coil is Pins 13 & 14). So when you go high on your input, your output will go on only for the delay setting on the timer. Once the timer picks, the output drops. Ala---Oneshot.

The whole thing is reset by releasing the input.

Here is an alarm circuit with a 15 minute anti-ignore timer and a supervisor override key switch. The operator can silence the alarm, but if he ingores it and does not correct the conditon, the alarm will sound again.

You can buy a one-shot relay.

http://www.idec.com/Products/ENG/PDF/U907_PDFs/G_Timers/G_Timers_SelectionGuide.pdf

Thanks everyone. Basicly what I trying to do is have the alarm go off every time a tank runs out, even if another is out. For example: all tanks are full. Tank 1 runs out the alarm goes off. I than push a button to silence the alarm. I do not refill tank 1. Tank 2 now runs out also. Again I want the alarm to go off.

With out a special timer relay or one shot relay, the only way I see to do this is to use a relay for each tank like this

tank1 cr1 cr1
----[ ]-------[ ]--------( )
cr1 l pb l
----[ ]-l l--[ ]--l
l cr1 alarm
l--[/]--------( )



tank2 cr2 cr2
----[ ]-------[ ]--------( )
cr2 l pb l
----[ ]-l l--[ ]--l
l cr2 alarm
l--[/]--------( )

Sorry for the cruedness. See any problem?

awh **** that did not come out right. It removed the spaces how do you write ladder logic on this?

Up at the top is a relay contact icon -||- that wraps around the ladder code. Also, don't preview the post, just click on submit, (unless that has been fixed by Phil).

You will then need four of the one shot pulse relays, plus one more relay. The Idec RTE pulse relays are $57.31 from Newark. Plus each relay will need a base, $8.65 each. You're already up over 260 bucks and you're not done yet.

At this point it becomes very attractive to use one of the PICO controllers or smart relays.

http://www.moeller.net/en/industry/switchgear/switch_control/easy/index.jsp#500

http://www.ab.com/plclogic/pico/pico.html

Both are the exact same unit. The 8in/4out unit lists for $209 from Newark, though the ones I buy from the local distributor are a bit less.


I have one in front of me right now, 8 in, 4 out. It took less than 15 minutes to set it up to do what you need to do. It might take all of 30 min. if its your first time to use one of these.
No software is required.

With the level switches wired to 1-4 and the N.O. silence button wired to 5, and the horn on Q1, here is the setup.
I1------TT1 (1s pulse)
I2------TT2 (1s pulse)
I3------TT3 (1s pulse)
I4------TT4 (1s pulse)
T1+-I5--{M1
T2|
T3|
T4|
M1|
M1------{Q1

Thats it. The entry is straight forward from the front keypad with the build in LCD display.
Heres a quick start manual:
http://literature.rockwellautomation.com/idc/groups/literature/documents/qs/1760-qs001_-en-p.pdf

A more detailed manual:
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1760-um001_-en-p.pdf

I agree with Alaric.

I know that you can get the basic Moeller "easy" relay online for under $100.

Also, if you are playing with 110 volts, Allen Bradleys ML1000 is probably still available for $99. I think it will do 6 in and 4 out. And it had FREE software.

regards.....casey