# Simple pulse delay question

Discussion in 'General Electronics Chat' started by Flyby, Jan 3, 2008.

1. ### Flyby Thread Starter New Member

Jan 3, 2008
3
0
I have a sensor which is a solenoid with a moving pressure pin inside it, and it's supplied with a constant current from a control unit. Every time the pin moves there's a pulse.

What I want to do is simply retard this pulse. I've been told the use of just a capacitor and a resistor would do it.

My logic tells me I should place the capacitor in series with the solenoid, and the resistor in parallel with the solenoid and capacitor, but it wouldn't be the first time my logic aint that logical.

2. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
219
What amount of time delay are you trying to achieve?

hgmjr

3. ### Flyby Thread Starter New Member

Jan 3, 2008
3
0
I need a very small delay, somewhere around 50 microseconds.

4. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
219
You may be able to get away with simple RC integrator as has been suggested. How wide is the pulse normally?

hgmjr

5. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Also, what does the pulse do? Does it activate something, or just get sensed? If the pulse is always the same, the RC network will give you a reasonably accurate delay. If it varies in magnitude, then you may need to detect it and use a small circuit to generate a delayed pulse.

6. ### Flyby Thread Starter New Member

Jan 3, 2008
3
0
It's just a rpm sensor so it only gets sensed. I'll give the RC integrator a shot. So it'll be the capacitor in series with the solenoid, and the resistor in parallel right?

Thanks

7. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
219
The resistor is placed in the signal line between the pulse source and the input to the next stage of the circuit. The capacitor connects between the downstream side of the resistor and ground. The time-constant in seconds is equal to R times C. Remember that it takes 5 of these time constants for the signal to transition from 0 to the normal maximum voltage and it also takes 5 time constants for the signal to transition back to 0 from the maximum voltage.

The input impedance to the next stage needs to be factored in since the series resistance forms part of a voltage divider that can attenuate your signal enough to cause a problem. Can you tell us more about what the pulse signal feeds?

hgmjr