setup of switching time

[udibeni]

hello to every one

i want to ask about setup of measuring switching time of SPDT-SWITCH POLE DUAL THROW

thak u all

udi

 

[blueroomelectronics]

What sort of test equipment do you have access to?

 

[crutschow]

An easy way would be to use a dual-trace oscilloscope, if you have access to one,

 

[alphacat]

Here is how I checked the switching times of my latching relay, and i'd love to receive some comments/verifications about that way.

I checked the switching time of the 'relay driver' + 'relay' - one time when latching and one time when unlatching.

Configuration:
* I connected 5V to NO pin of the relay, and a pull-down resistor to the Pole pin (also called Common pin).
* The relay driver was connected to the Relay's coil.
* The Pole was connected to the NC pin.

This is how I checked the Latching time:
In order to switch the relay (from NO to NC) I had to trigger the relay driver input.
Therefore:
A. One probe was measuring the latching input voltage of the relay driver.
B. Second probe was measuring the Pole pin's voltage.
C. I had the scope to freeze the picture when probe B's voltage was rising from 0V to 5V.

At this stage, I triggered the latching input voltage, and measured the time difference between A. and B. .

 

[crutschow]

One time I had the problem of measuring the operate time of a solenoid air valve with no contacts, which at first seemed rather difficult. But after some thought, I tried a small resistor in series with the coil to measure the coil current with an oscilloscope. From the trace of the coil current you could see the inductive rise of current after voltage application with a little blip in the current after about 50ms. The blip was caused by the slight change in coil reactance when the solenoid hit the closed position.

 

[alphacat]

wow.
What do you mean that the solenoid hit the closed position?

 

[crutschow]

wow.
What do you mean that the solenoid hit the closed position?

The solenoid value was normally open (air could flow). When power was applied the solenoid closed the valve. The current blip was when the value reached the closed position and the solenoid suddenly stopped moving.

 

[alphacat]

Oh I see, thanks.

By the way, in regular relays (ones with contacts), for the relay to change its state (meaning to change the location of the pole), the coil needs to saturate (become a short)?
I was wondering if its possilbe to determine the coil's value by the switching time thats specified in the spec.

For example, in my relay it is said that the maximal switching time is 15msec, and that the coil resistance is 25ohm (+- 5%), so can is it correct to say that:
L = 15msec * 25ohm = 0.375H ?

 

[crutschow]

Oh I see, thanks.

By the way, in regular relays (ones with contacts), for the relay to change its state (meaning to change the location of the pole), the coil needs to saturate (become a short)?
I was wondering if its possilbe to determine the coil's value by the switching time thats specified in the spec.

For example, in my relay it is said that the maximal switching time is 15msec, and that the coil resistance is 25ohm (+- 5%), so can is it correct to say that:
L = 15msec * 25ohm = 0.375H ?

The coil doesn't have to saturate to close the poles, but it will likely be near saturation when the coil is at it's rated current.

Your inductance calculation assumes the the relay closes in one time-constant, which is not necessarily true, since the time is related to both the coil inductance and the time it takes to mechanically move the contacts. But the calculation may give you a rough ball-park figure for the inductance.

 

[alphacat]

Thank you very much.