Cheap Millisecond Timer

[big john]

Wondering if anyone had some solutions for a digital panel-mount timer that was accurate down to a millisecond?

Alternatively, I know totalizer meter can be very precise, is there a workaround to make one time a very short duration?

The kicker is that I have a small budget tp spend, so gotta keep solutions less than $200. Thanks.

 

[Ingenieur]

What you doing with it?
how is it started, stopped and reset?

 

[Ingenieur]

https://www.wolfautomation.com/inde...ac-spdt-npn/?gclid=CL68g-T29NECFcmFswod7C4KMw

 

[big john]

I appreciate you looking, but unfortunately it appears the best accuracy for that model is ~30 milliseconds.

Maybe I need a microsecond timer, because I literally need accuracy down to 1 millisecond.

Ideally this is triggered by opening/closing contacts, but if I had to apply voltage I could make that work.

 

[Ingenieur]

Different model same spec https://www.wolfautomation.com/products/timers-counters/3-in-1-timer-counter-tachometer-relay-output
10000 count/sec
0.0001 sec/count or 0.1 ms/count
so 1 ms = 10 counts, good resolution
can display in ms
am I misreading the spec
???

 

[Ingenieur]

I appreciate you looking, but unfortunately it appears the best accuracy for that model is ~30 milliseconds.

Maybe I need a microsecond timer, because I literally need accuracy down to 1 millisecond.

Ideally this is triggered by opening/closing contacts, but if I had to apply voltage I could make that work.

what are you timing?
circuit breakers are in the 3-5 cycle range 50 ms
even a transient peaks in 1/2 cycle or 8.3 ms

a ballistic timer can measure to 0.1 ms
4000 fps in 2' is 0.5 ms

usec is light speed realm lol

 

[mpoulton]

For timers that fast, you will have to be careful about your contacts. Mechanical contacts bounce when they close, causing a series of pulses before they settle down and stay closed. With a sub-millisecond timer, those bounces will cause re-triggering and unpredictable behavior if your system does not take measures to avoid it.

 

[big john]

I'm doing breakers, but that's why I need the accuracy.

Yeah, it migh be as much as 50mS, but if I can't reproducibility capture that value, and less, very precisely it's no bueno.

My phone refuses to load that webpage properly, but the PDF I found for that model said +-30ms.

 

[Ingenieur]

1 cycle = 16.7 ms
f = 60 cycle sec

to capture that accurately you need 2 x that or 120 samples/sec
that timer does 10000 cps



We use one of these https://www.atecorp.com/products/multi-amp/ms-2
measures to 1 ms
0.06 cycles

 

[big john]

Yeah, we own one of those. The problem is it has no external start trigger for the timing circuit:

I'm using a separate DCmV supply to cause the trip units to pickup, and the trigger needs to start on a control contact closure and stop when the breaker trips.

What about trying to use a process totalizer to count 60Hz mains frequency?

 

[gar]

170203-2018 EST

I don't understand parts of this thread.

What I think is being ask is:

1. An inexpensive time measuring device is needed to measure up to a full scale value of 50 mS, with a resolution better than 1 mS. What resolution is really required? This somewhat relates to what accuracy is required. Is accuracy to be based on reading or full scale?

2. Time measurement is to be initiated by a contact closure, or possibly by some millivolt trigger signal that is used to initiate the trip mechanism of a breaker.

3. Time measurement is to be terminated by opening of the breaker.

4. My preference would be an oscilloscope. I did this with an ordinary oscilloscope and a camera back in the early 60s. Today I would use a digital scope.

5. A simple way to measure short times is with a current source, capacitor, and high impedance meter. The early part of an RC charge curve is approximately linear with respect to time. A high voltage source and resistor is an approximate current source to a capacitor when the voltage to the capacitor is small compared to the source voltage.

Probably a better approach is to use an operational amplifier with a resistor and capacitor as an integrator with a gated voltage source for the time period and a digital voltmeter on the output. This can be a relatively low cost approach.

Contact bounce mentioned above will cause some small problems.

6. Knowledge of your real required accuracy is important to any selection of a method for your measurement, and how the start and stop signals are created. I have used a Simpson 260 as a ballistic galvanometer to make some millisecond measurements of a Potter and Brumfield timer relay. Not highly accurate, but it worked.

7. Also note that an instrument called a counter/timer could work. But it is way overkill. And a jungle out there to figure what is available. Technical descriptions are very poor. Too much clutter and too little information.

I went looking for BK Instruments, they were in the past a low cost supplier, did not find a counter/timer, only frequency meters. An old model would be a possibility.

Found a company GW Instek with a model GFC 8270 H that is in the $ 400 range. Could be tricky to use because of its high frequency sensitivity. Would require filtering at its inputs.

There are a lot of PC based counter/timers. I did not look at any specs.

.

 

[gar]

170203-2357 EST

Another method to measure the time.

Build a 555 (timer) oscillator. Use the free run mode either as a pulse generator, or square wave source. Possibly run at 10 kH which will provide timing measurement with a resolution of 0.1 millisecond, 100 microseconds.

Use some means to use your start and stop signals to create an on gate during the time interval to be measured.

Use an electronic counter to count pulses from the 555 oscillator selected by the gate. The counter must be able to count the gated pulses and probably needs to be at least 3 digits.

If you want greater resolution use 100 kH, and at least a 4 digit counter. This provides 10 microsecond resolution.

I think the greatest experimental timing errors will result from the means to get your start and stop information.

Base timing accuracy is set by the frequency of the 555 timer.

.

 

[GoldDigger]

Yeah, we own one of those. The problem is it has no external start trigger for the timing circuit:

I'm using a separate DCmV supply to cause the trip units to pickup, and the trigger needs to start on a control contact closure and stop when the breaker trips.

What about trying to use a process totalizer to count 60Hz mains frequency?

The only problem with that is that even if you pulse rectify it to get 120Hz that is still only ~8 ms resolution.


mobile

 

[Besoeker]

Yeah, we own one of those. The problem is it has no external start trigger for the timing circuit:

I'm using a separate DCmV supply to cause the trip units to pickup, and the trigger needs to start on a control contact closure and stop when the breaker trips.

What about trying to use a process totalizer to count 60Hz mains frequency?

Do you need it to be a fixed panel meter?
I use a digital storage scope that has a resolution in the ns range and it can be externally triggered. The data can be downloaded via the RS232 port to a spreadsheet or simmilar app. Would something like that give you the information you want/need?

 

[big john]

Right now to do breaker contact timing we haul out extremely expensive, very bulky, very tempermental laptop-controlled protective relay testers. They are way overkill and can be very frustrating.

For this application I literally just need something that can watch to see if a control pushbutton closes, and then counts until the breaker contacts open.

I was hoping that a market existed for small, single-channel high accuracy timers, I would just toss one in a project box.

Instantaneous trips occur at values of less than 50mS, so it definitely needs to be repeatably accurate below that range. Maybe 1mS is too ambitious.

 

[Ingenieur]

What kind of relay takes mV dc?
still not clear on what you are testing
most take 5 or 1 A ct's

not sure I would have confidence in a kluged up test kit
you can use the multi-amp output to trigger the relay
even in V input just get a variable resistor and run i thru it in series and parallel the R across the relays voltage input

if I were paying for this service (and I have) I would want to see the procedure and equipment
and would require the equipment be built, certified and calibrated for the purpose and the operator trained to perform it

 

[Ingenieur]

Set-up?

dc supply
timer
push button
ac for the dc supply and timer

feed dc to pb and relay sensing input
also to dry contacts on relay? To start timer when tripped?
so the actual cb is not tested?
nor the actual i sensing system? Ct's, etc

we typically test at 3 points
3 x i rated
8 times
16 times
that way we get a response curve

on small breakers loop thru ct's, can get up to 700 A iirc with 1 loop
can loop it 2 or 3 times, sometimes 5

sometimes feed current into relay ct input
prefer looping the ct

 

[gar]

170204-1117 EST

big john:

We still have no definition of accuracy. We have a full scale value of 50 mS.

If one uses a simple RC (resistance-capacitance) timing circuit and set full scale to be 0.1 time constant, then for a 50 mS full scale we want a time constant of 500 mS. Using a 10 ufd capacitor with a shunt across the capacitor of a 10 megohm DVM we have a discharge time constsant of 100 seconds. Probably long enough to get an adequately accurate peak voltage reading ( could also enhance this reading by using the DVM peak reading capability).

For 0.5 V on the 10 ufd capacitor at 50 mS, then for a DC source voltage of 5 V we pick a 50,000 ohm charging resistor. Note: 10 mS produces a peak voltage of 0.1 V, and 1 mS 0.01 V.

A polypropylene or polystyrene capacitor needs to be used. Low leakage.

You could use a 9 V battery as the voltage source and adjust the resistance for time calibration.

A variable resistor with a fixed resistor, a capacitor, a 9 V battery, and an existing DVM is quite small and inexpensive. Also a reset switch consisting of a normally open push button with gold contacts to short the capactor.

To the above there needs to be a contact closure (probably a small reed relay) to occur during the desired time of measurement. Not enough information yet to provide any suggestions. This area is going to generate some time errors that need to be considered in calibration.

.

 

[big john]

What kind of relay takes mV dc?

DC breakers look at DCmV shunts.

So the actual cb is not tested?
nor the actual i sensing system? Ct's, etc.

If you apply appropriate signal levels into the trip unit and the breaker operates within the prescribed time, that is the full extent of any secondary-injection test. No difference here.

Gar, I appreciate the thought that went into that explanation, but I am only looking for an off the shelf solution for the timer.

 

[gar]

170204-1618 EST

big john:

A search for digital scopes produces a jungle of worthless non-detailed information. Google has become an almost worthless search means in certain areas. Mostly advertizing for companies like Amazon.

I have no idea whether the following would work to make your measurement, be durable, or reliable, but it is cheap.

One channel could sync from the mV trigger, and a second channel look at the breaker output.

[h=1]SainSmart Mini DSO DSO203 Nano ARM Portable Digital Handheld Oscilloscope, 4 Channels, 72MHz Bandwidth[/h]