Dose the following circuit provide an on delay for CR5, or off delay, or both?
I'm trying to figure out the purpose of the time constant RC.
The resistor is 15k and the cap. is 47ufd.
Coil resistance is 1k.
Thanks

 

Gut feeling from schematic layout would be snubber to reduce switching noise from inductive load of coil, but those values are way higher than I would've expected based on the [very few] snubber circuits I've known.

FWIW, I have almost zero experience reading ladder logic, so I could be totally misreading all of that!

 

With no voltages, no currents, and half the schematic missing, that looks like a snubber, badly done.
For instance, if the logic elements are all relays and mechanical switches, you don't need snubbers. In this case, that's good because you basically don't have any.

A lot more information might reveal why those parts are there and whether they are effective. As for now, it's mostly guessing.

 

Sorry, I will explain the circuits function.
When the MASTER ON push button is depressed, CR3 will come on, dropping CR5 out.
When CR5 goes off, then a check is made to ensure the contacts between terminals A3 and A4 are closed.
This will allow CR4 to come on, if the check is OK.
When CR4 comes on the check is good, then CR5 will come back on.
Then when the push button is released, CR5 needs to be maintained on, so I'm assuming the RC time constant is there to maintain CR5 while CR4 contact opens and waiting on CR3 contacts to close.

But I'm don't know if the RC circuit is for ON delay or OFF delay.

 

Still no voltages or currents given. Can you understand that there is a difference between a 24 VAC controller board and a 240 volt appliance? Those alleged snubbers might do something at 240 volts, where the resistors and capacitors pass 10x the current they pass at 24 volts, but they still aren't time delays.

 

it could only be an off delay if it is in fact a delay

 

24v DC

Still no voltages or currents given. Can you understand that there is a difference between a 24 VAC controller board and a 240 volt appliance? Those alleged snubbers might do something at 240 volts, where the resistors and capacitors pass 10x the current they pass at 24 volts, but they still aren't time delays.

 

I tend to get myself turned around when applying these equations, but I believe the time constant for the coil, resistor, and cap together is 44ms. So assuming 63% of normal coil voltage is enough to keep the relay engaged, it would hold the relay active for an extra 44ms. I believe the delay applies in both directions, so it would also delay relay activation by 44ms (give or take, depending on what percentage of rated voltage it actually takes to activate the relay)

Does a ~44ms delay make sense in this circuit? Is that enough to cover the gap in response time between the other relays?

 

Does a ~44ms delay make sense in this circuit? Is that enough to cover the gap in response time between the other relays?

Almost all relays function in less than 10 ms. If you are right, 44ms is significant.
But the power hits both ends of CR5 instantly.
I'm with @strantor . If there is any delay, it's a lag during shut-off.

 

Almost all relays function in less than 10 ms. If you are right, 44ms is significant.
But the power hits both ends of CR5 instantly.
I'm with @strantor . If there is any delay, it's a lag during shut-off.

Not surprisingly, I got a few concepts mixed up in my head on this one.

I would trust both of you on this regardless, but just for grins (and in the hopes of maybe better understanding it,) I simmed it. The sim shows no substantial effect on coil current unless the resistor gets WAY smaller or the capacitor gets WAY bigger. Thanks for keeping me honest!

 

Dose the following circuit provide an on delay for CR5, or off delay, or both?
I'm trying to figure out the purpose of the time constant RC.
The resistor is 15k and the cap. is 47ufd.
Coil resistance is 1k.
Thanks

There is something about the values stated I can not get to fit.

However, with a 15 Ω resistor, the 47 uF capacitor can hold a 24 V / 1000 Ω relay coil drawn in the 44 mSec specified in the latest postings.

 

Thanks for keeping me honest!

I don't sim, but I have 50 years of experience.
My instincts told me this "snubber" is B.S. but I didn't run the math because I was sure it would sim out as crap.

 

I tend to get myself turned around when applying these equations, but I believe the time constant for the coil, resistor, and cap together is 44ms. So assuming 63% of normal coil voltage is enough to keep the relay engaged, it would hold the relay active for an extra 44ms. I believe the delay applies in both directions, so it would also delay relay activation by 44ms (give or take, depending on what percentage of rated voltage it actually takes to activate the relay)

Does a ~44ms delay make sense in this circuit? Is that enough to cover the gap in response time between the other relays?

 

Yes, I do believe 44ms would be enough.
I checked the specs on the relay and it pulls in at 18v, and releases at 4v.
The activation time for pulling in the contacts are 16ms and the deactivation is 7ms.

 

How did you come up with 44ms?

 

That diagram you posted - is that (um) chip a micro controller?

Better yet, what are you trying to accomplish? Are you just curious? (which is always a good thing when you don't hurt yourself) Are you trying to use this device for something other than what it was designed to do? Are you trying to bastardize it for some other purpose? There's a lot of guys here who are really sharp on those sorts of things. I got a lot of help modifying a 12 volt power supply to be able to put out 13.6 volts. These guys are sharp as tacks. (then again, I've seen some guys who were as sharp as a fuzzy tennis ball)

Something that has me wondering is the designations of CR3, CR4 and CR5 (and other components) - they are used in multiple locations. To me (and what do I know?) there should be only one CR3, one CR4 and one CR5. Something about your drawing I don't understand. Also, what looks like capacitors and variable caps with what appeared to me (I'm probably mistaken) is the relay that is supposed to control the light curtain. It looks to me like yet another capacitor.

 

How did you come up with 44ms?

I was hoping everyone would just forget I said that!

Ignore that number. After running the sim and re-thinking things, I realized I had it all wrong. That number came from combining the 15k resistor and 1k coil resistance in parallel (a mistaken approach,) and using the resulting ~937ohms in the RC calculation.

More importantly, the sim helped me see why #12 and strantor were right. With 15k ohms in the RC circuit, it just can't do much.

When power is applied to that portion of the circuit, the coil and the RC circuit are in parallel, so they both see the full 24VDC immediately. The only way the RC circuit can effect the coil is if there's a severe limit on the available current (series resistance between voltage source and this leg.) Even then, with 1k vs 15k, the coil will take most of the available current and there will be no tangible effect.

When the relay opens, removing power from this leg, the cap will be charged with 24V and will discharge through the coil, but since the 15k and 1k are in series for the cap's discharge, current through the coil will start at 1/16th of its normal operating current and drop rapidly from there.

@#12, Please let me know if I've got the basic concepts right this time. I don't get hands on with all these circuit variations as often as I'd like, but I learn a lot from these mental exercises, and I want to make sure I'm learning right.

 

That diagram you posted - is that (um) chip a micro controller?

Better yet, what are you trying to accomplish? Are you just curious? (which is always a good thing when you don't hurt yourself) Are you trying to use this device for something other than what it was designed to do? Are you trying to bastardize it for some other purpose? There's a lot of guys here who are really sharp on those sorts of things. I got a lot of help modifying a 12 volt power supply to be able to put out 13.6 volts. These guys are sharp as tacks. (then again, I've seen some guys who were as sharp as a fuzzy tennis ball)

Something that has me wondering is the designations of CR3, CR4 and CR5 (and other components) - they are used in multiple locations. To me (and what do I know?) there should be only one CR3, one CR4 and one CR5. Something about your drawing I don't understand. Also, what looks like capacitors and variable caps with what appeared to me (I'm probably mistaken) is the relay that is supposed to control the light curtain. It looks to me like yet another capacitor.

Google "relay ladder logic" and it will make a lot more sense! What look like caps and variable caps are the symbols for NO and NC relay contacts. The relay coils are the circles. Thus, each relay can have three, or more depending on relay type, separate symbols on the diagram.

 

It's called ladder logic.
The components you see are relays and their associated contacts.

 

Thanks to all.
I'm satisfied that the circuit is being used for and off delay, so CR5 will not drop out when CR4 and CR3 switch.
Again thanks for everyone's input.