Pulser input to a timer relay signal input not shutting down.

Thread Starter

daytona

Joined Jan 15, 2021
31
Thanks in advance for any help.
I have a 12vdc output from a mechanical pulser that runs to a digital counter and also runs to a digital timer relay. I need the timer to count down when pulses stop. What is happening is that the timer counts down perfectly when the pulser stops pulsing on the off pulse (or between pulses) but fails to count down when the pulser stops on a 12 Vdc pulse.

I am using a Schneider 821TD10H-UNI Time delay relay. I have tried the Off delay with "s" break and I tried Retriggerable one shot with "s".

I need the relay to switch states after 15 seconds of no continuing pulses.
I tried putting a cap, resistor, and 1 meg ohm in the circuit but I probably wired it wrong
 

LesJones

Joined Jan 8, 2017
3,078
Can you not just differentiate the pulses from the mechanical pulser so you generate a short pulse from the low to high transition from the pulser. this would only need a capacitor, a resistor and a diode. (The diode is to clamp the negative pulses that would be generated on the high to low transition.

Les.
 

Thread Starter

daytona

Joined Jan 15, 2021
31
Can you not just differentiate the pulses from the mechanical pulser so you generate a short pulse from the low to high transition from the pulser. this would only need a capacitor, a resistor and a diode. (The diode is to clamp the negative pulses that would be generated on the high to low transition.

Les.
My bad I said "I tried putting a cap, resistor, and 1 meg ohm in the circuit but I probably wired it wrong" I meant cap, resistor and diode. I will see if I can make a schematic to attach. I didn't have a ground to send the pulse to.
 

eetech00

Joined Jun 8, 2013
2,292
Thanks in advance for any help.
I have a 12vdc output from a mechanical pulser that runs to a digital counter and also runs to a digital timer relay. I need the timer to count down when pulses stop. What is happening is that the timer counts down perfectly when the pulser stops pulsing on the off pulse (or between pulses) but fails to count down when the pulser stops on a 12 Vdc pulse.

I am using a Schneider 821TD10H-UNI Time delay relay. I have tried the Off delay with "s" break and I tried Retriggerable one shot with "s".

I need the relay to switch states after 15 seconds of no continuing pulses.
I tried putting a cap, resistor, and 1 meg ohm in the circuit but I probably wired it wrong
What is the pulse rate of the mechanical pulser?
 

Thread Starter

daytona

Joined Jan 15, 2021
31
What is the pulse rate of the mechanical pulser?
It is pulsing at the rate of fluid being pumped so it will vary from 1 pulse per second to 20 pulses per second. The timer resets every time it senses a pulse and the wait time starts over. Once the pulses stop coming the timer is supposed to count to 15 seconds and stop the current flow. I will try to go back to the original thread and give more info.
 

Thread Starter

daytona

Joined Jan 15, 2021
31
Thanks in advance for any help.
I have a 12vdc output from a mechanical pulser that runs to a digital counter and also runs to a digital timer relay. I need the timer to count down when pulses stop. What is happening is that the timer counts down perfectly when the pulser stops pulsing on the off pulse (or between pulses) but fails to count down when the pulser stops on a 12 Vdc pulse.

I am using a Schneider 821TD10H-UNI Time delay relay. I have tried the Off delay with "s" break and I tried Retriggerable one shot with "s".

I need the relay to switch states after 15 seconds of no continuing pulses.
I tried putting a cap, resistor, and 1 meg ohm in the circuit but I probably wired it wrong

More info: This is for a pumping operation and we have a requirement that the pump must stop if the fluid stops for any reason so that the pump will not be damaged. The pulse rate is from 1 pulse per second to 20 pulses per second. The usual rate will be about 17 but that doesn't seem to be any problem. The problem comes in when the pulser stops on a pulse so the output to the times "S" is 12 Vdc. The boss doesn't want a flow switch in the system because it will reduce the flow. I will post my crude schematic from excel again here so all can see it. I am new to these threads so let me know if I am posting incorrectly.
I need to try to solve this by tomorrow because our customer will be here to test the systempulser timer.jpg
 
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Thread Starter

daytona

Joined Jan 15, 2021
31
My bad I said "I tried putting a cap, resistor, and 1 meg ohm in the circuit but I probably wired it wrong" I meant cap, resistor and diode. I will see if I can make a schematic to attach. I didn't have a ground to send the pulse to.
Les, do you know how to wire those components? See how I did it. mine didn't work
 
Last edited:

LesJones

Joined Jan 8, 2017
3,078
This is the basic idea.
010321.jpg

You will need to supply details of the output of the pulser circuit. For example is it just a switch contact between say +12 volts and the output or something that provides pull up and pull down ? You will also need to give the specifications of the input pulse for the counter. This will be the voltage levels, the minimum pulse input duration and the input impedance of the the counter.
I have done a rough sketch of the waveforms at points in the circuit. A is the square wave from the pulser. B is the differentiated waveform and C is it with the negative going pulse removed. I would guess at values of 100 nF for the capacitor and 10K for the resistor but this will probably have to be adjusted to suit the input of the counter. If the output of the pulser is just switch contacts to +12 or ground then it will need a resistor adding pulling it to the other rail. (Say 1K as a starting point.

Les.
 

eetech00

Joined Jun 8, 2013
2,292
Here is an alternate circuit that includes contact filtering and buffering.
This uses smaller C values and C3/R7 adjusts the pulse width.

1614640885610.png
 

Thread Starter

daytona

Joined Jan 15, 2021
31
This is the basic idea.
View attachment 231819

You will need to supply details of the output of the pulser circuit. For example is it just a switch contact between say +12 volts and the output or something that provides pull up and pull down ? You will also need to give the specifications of the input pulse for the counter. This will be the voltage levels, the minimum pulse input duration and the input impedance of the the counter.
I have done a rough sketch of the waveforms at points in the circuit. A is the square wave from the pulser. B is the differentiated waveform and C is it with the negative going pulse removed. I would guess at values of 100 nF for the capacitor and 10K for the resistor but this will probably have to be adjusted to suit the input of the counter. If the output of the pulser is just switch contacts to +12 or ground then it will need a resistor adding pulling it to the other rail. (Say 1K as a starting point.

Les.
Les, I will try the circuit.
The counter is fine it worked in a past project and is working great in this project. It is just the timer relay that has a problem. The counter only counts when pulses switch from high to low. The timer whenever it sees a +voltage it resets the countdown and doesn't allow it to count down. Perhaps I went about this all wrong. The pulser is made by www.intconsys.com It is model SP1 smart pulser. the switching voltage is 12vdc max current 300ma and on resistance of 23 to 35 ohms. It is a microprocessor
 
Last edited:

Thread Starter

daytona

Joined Jan 15, 2021
31
Here is an alternate circuit that includes contact filtering and buffering.
This uses smaller C values and C3/R7 adjusts the pulse width.

View attachment 231821
EETECH, thanks for your hard work. I don't think we need to shorten the pulse or eliminate bounce (I could be wrong) but when the pulse stops on a 0 Vdc there is no problem. When it stops on a 12 Vdc it stays there until total power is removed. I see a red and green led flash in that case as the timer is still getting 12 vdc and won't count down
 

eetech00

Joined Jun 8, 2013
2,292
EETECH, thanks for your hard work. I don't think we need to shorten the pulse or eliminate bounce (I could be wrong) but when the pulse stops on a 0 Vdc there is no problem. When it stops on a 12 Vdc it stays there until total power is removed. I see a red and green led flash in that case as the timer is still getting 12 vdc and won't count down
Here's a circuit using LesJones suggestion.
For 20hz (20 pulses per second), pulse width is 25m@50% duty cycle. This is used in the simulation shown below.
However, the Timer datasheet states 50ms trigger time.....confusing...
You'll need to figure out the actual pulse width of the pulser. The output pulse width to the timer needs to be adjusted shorter than the pulse width of the pulser output, at the fastest pulse rate, but long enough to reliably trigger the timer. The mosfets shown at the right "square up" the RC differentiated pulse. The mosfets may or may not be needed.

1614666222467.png
 

LesJones

Joined Jan 8, 2017
3,078
Hi datona,
I had assumed that the counter an timer were part of the same unit and they were built using logic ICs (Or a microcontroller performing both counting and timing functions.) so I assumed they would respond to quite short pulses. From the link to the pulser and the other products on the website it looks like the counter you are using is mechanical. If this is the case then the component values I suggested will probably give too short a pulse. From the added information the circuits (Either mine or eetecch00's) only need to go to the timer. Can you confirm that the pulser output is just a set of contacts and show how it is connected to the counter. I suspect that the counter input could be a solenoid in the mechanical counter. Can you give information on the timer input circuit so the design can be made to suit this.

Les.
 

Thread Starter

daytona

Joined Jan 15, 2021
31
Hi datona,
I had assumed that the counter an timer were part of the same unit and they were built using logic ICs (Or a microcontroller performing both counting and timing functions.) so I assumed they would respond to quite short pulses. From the link to the pulser and the other products on the website it looks like the counter you are using is mechanical. If this is the case then the component values I suggested will probably give too short a pulse. From the added information the circuits (Either mine or eetecch00's) only need to go to the timer. Can you confirm that the pulser output is just a set of contacts and show how it is connected to the counter. I suspect that the counter input could be a solenoid in the mechanical counter. Can you give information on the timer input circuit so the design can be made to suit this.

Les.
Thanks, the counter is a digital that can take many different inputs. It works fine. Forget that I mentioned the counter unless feeding 2 or 3 devices causes a problem. When I can get back on the machine I will eliminate the other 2 devices and try to concentrate on the timer.
 

Thread Starter

daytona

Joined Jan 15, 2021
31
Here's a circuit using LesJones suggestion.
For 20hz (20 pulses per second), pulse width is 25m@50% duty cycle. This is used in the simulation shown below.
However, the Timer datasheet states 50ms trigger time.....confusing...
You'll need to figure out the actual pulse width of the pulser. The output pulse width to the timer needs to be adjusted shorter than the pulse width of the pulser output, at the fastest pulse rate, but long enough to reliably trigger the timer. The mosfets shown at the right "square up" the RC differentiated pulse. The mosfets may or may not be needed.

View attachment 231843
I must not know enough to communicate this. If The pulser stops on the pulse it becomes a steady 12vdc and the timer won't start to count down. Forget the pulse width or freq. It becomes on solid. At this point I am going to have to tell the customer that the project is not going to be done for some time. We will look for a flow switch and install it unless we can come up with an electronic solution. And the boss is not going to go for a circuit board. He had a hard time letting me put a diode and kick back diode in another part of the system. He likes din rail solutions. Thanks again for your help
 

Thread Starter

daytona

Joined Jan 15, 2021
31
Les, I will try the circuit.
The counter is fine it worked in a past project and is working great in this project. It is just the timer relay that has a problem. The counter only counts when pulses switch from high to low. The timer whenever it sees a +voltage it resets the countdown and doesn't allow it to count down. Perhaps I went about this all wrong. The pulser is made by www.intconsys.com It is model SP1 smart pulser. the switching voltage is 12vdc max current 300ma and on resistance of 23 to 35 ohms. It is a microprocessor
Les, I tried the circuit and it totally killed the 12 vdc even when pulsing. I didn't have the correct cap and used a 4.7 uF. After the customer leaves I will try to correct. I will just tell the customer it will be fixed before we ship. Thanks again for all your time and effort. I learned a lot.
 

eetech00

Joined Jun 8, 2013
2,292
I must not know enough to communicate this. If The pulser stops on the pulse it becomes a steady 12vdc and the timer won't start to count down. Forget the pulse width or freq. It becomes on solid.
We are aware that when the pulser stops, sometimes its output remains at 12v. The purpose of the differentiator is to overcome this. Each time the pulser output "rises" from 0v to 12v, the differentiator circuit outputs a short pulse that rises, and after a short duration, quickly falls. So...with the differentiator circuit connected between the pulser and timer, even though the pulser output may stop at 12V, the timer "S" terminal will see 0v. When the Pulser begins to "pulse" again, the differentiator will output a rising pulse on the first rise of the pulser output and trigger the timer.

But....for this to work reliably, specifics on the Pulser output waveform and Timer input waveform is required so that the differentiator circuit can properly "condition" the output signal sent to the Timer.

Hope that helps....
 
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