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Bob D.
10-25-2011, 12:20 AM
I have a simple run time meter wired into my air compressor so I can keep track of the actual usage to see when it's time to change the oil. No big deal, it's just a simple clock mechanism that drives a mechanical digital readout.

A friend needs a similar gizmo, EXCEPT that he needs it as a separate discrete unit, not wired into the device to be monitored. Something like this: run time totalizer plugs into wall outlet, device gets plugged into outlet on totalizer, totalizer only increments when device is running.

Simpson Instruments sells a totalizer that get wired in Parallel with the unit to be monitored, but I don't understand how that meter knows when the device is on or off, don't see any current sensing loop in their meter.... :confused: ???

Any help greatly appreciated. He needs 4 or 5 of these for equipment in a science research lab, so invasive mods would void warranties and potentially cause headaches for/from the field service reps.

A good opportunity to help my buddy and make a few bucks to fund my home shop at the same time :D

any ideas?

armedandsafe
10-25-2011, 12:54 AM
We had a similar situation back in the late 60s, early 70s. I found an analog clamp-on ammeter which had a switch contact in the needle mechanism. When the meter hit a certain amperage, it would close the low voltage switch. I wired that switch to a low voltage relay and used the relay to drive a strip recorder.

If you can find those ammeters, you can rig them to a modern recording counter/timer.

Today, I would probably use one lead to the outlet, wrap transformer wire around it to give me a current flow relative to the current in that lead. Then I would feed that to an SCR or something similar to trigger the counter.

Or, I would use one of the hand-held current detectors used to trace wiring buried in walls and put a photocell over its activity light.
http://extech.com/instruments/resources/manuals/DVA30_UM.pdf

Here is an outfit which can probably help you.
http://www.crmagnetics.com/

But, that is my 50 years of electronic design experience speaking. If you have questions during your development, feel free to PM me or email me.

Pops

macona
10-25-2011, 02:18 AM
SCRs latch on. Not going to work here.

Make up a small box with a little current transformer. Rectify it with a diode and drive a transistor with it.

There are companies who sell such a device ready to go. Honeywell makes them:

http://sensing.honeywell.com/index.cfm?Ne=3025&ci_id=154286&N=3036&la_id=1

You might be able to get away with wrapping the hot wire around a reed switch as well. Not sure if it will chatter though.

Joel
10-25-2011, 02:29 AM
How about a current sensing power strip?
I don't know the current requirements, but I use something similar to this to turn on stereo equipment when the main amp is powered up:
http://e3living.com/smart-strip-7-outlet-energy-saving-surge-protector

Here is a fancier unit with 12v:
http://www.amazon.com/Niles-CS12V-Current-sensing-12-volt-trigger/dp/B000VI50OM

Paul Alciatore
10-25-2011, 02:33 PM
You need a current sensing relay or circuit to do the same thing. Of course, solid state is better. It is a device to be attached to the power line in an industrial environment so a complete device that is UL listed is probably best.

There are many devices which can sense current: relays, current transformers, a simple low value series resistor and differential amp connected across it, etc. Finding a commercial device will be a bit more difficult and you will probably be more successful if you look for the current sensor and the timer as separate devices. You may have to add a power supply or power transformer (wall wart) if either or both of these need lower Voltage or a DC supply. Here is a start that I found searching for "current sensor".

http://www.serelays.com/time_delay_sensor_relays.php

Timers are everywhere, just do an internet search or look on electronic sites like Digi-Key. Mouser, Newark, etc. Connect the timer to the output of the sensing circuit. It would be best if this is a low voltage timer as it would not need UL approval.

kennyd4110
10-25-2011, 03:04 PM
Do a Google for "Vibration Hour Meter" like this: http://www.amazon.com/Hardline-Products-HR-8065-Vibration-Meter/dp/B003RB0IAQ

Willy
10-25-2011, 03:29 PM
Like kennyd4110 said, a vibration activated hour meter works well, even on electric motors.
You didn't state what type of equipment this is for so I'm not sure if this even applicable for you needs.
If it is to be used on a piece of electronic equipment that does not produce any vibratory stimulus then obviously this is a no go.

I have used hour meters from ENM before and they do work well.

http://news.thomasnet.com/fullstory/Hour-Meters-are-vibration-activated-31031



Applications include diesel equipment, air compressors, electric motors, rental equipment, amusement park rides, go-carts, and construction machinery.




Ebay has similar units for 12-15 dollars.

Bob D.
10-26-2011, 03:52 PM
How about a current sensing power strip?
I don't know the current requirements, but I use something similar to this to turn on stereo equipment when the main amp is powered up:
http://e3living.com/smart-strip-7-outlet-energy-saving-surge-protector

Thanks! I hadn't considered this approach. I'll check the current requirements with my buddy. I can easily and cheaply get a 12 VDC hour meter and power it with a wall wart. No AC wiring on my part, and if the wall wart or outlet strip craps out, he can easily replace them by himself. :D

The equipment is a biochem lab in a university, so he's probably checking the hours that lamps in spectrometers are in use. Can't see for myself, he's in Wisconsin and I'm in New Jersey.

Vibration sensing wouldn't work in this application, but that is another great idea to file away for future reference... Thanks to everyone who took the time to reply!:)

armedandsafe
10-26-2011, 05:05 PM
SCRs latch on. Not going to work here.

You are right that the SCR would latch on for <1/120 second.

Pops

macona
10-26-2011, 05:50 PM
Oh, I was thinking of a little battery powered self contained lcd counter.

armedandsafe
10-26-2011, 08:21 PM
Oh, I was thinking of a little battery powered self contained lcd counter.

My apologies, sir. I was feeling a bit snarky and it resulted in that smart-A remark. :D

Having now done acursory search for off the shelf items for this problem, it appears that there are several potential solutions. The best ones don't require wiring into the delivery circuit. I still like the idea of isolating one leg and using the presence of current trigger the counter.

Pops

SteveF
10-26-2011, 08:53 PM
Maybe use a Kill A Watt?

http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU

Doesn't measure hours directly but once you run it for an hour to learn the energy usage for that device, simple math to take the total kilowatts used and divide. Warning - if the power goes out, all the counters reset to zero.

Steve

Bob D.
10-26-2011, 09:58 PM
Maybe use a Kill A Watt?

http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU

Doesn't measure hours directly but once you run it for an hour to learn the energy usage for that device, simple math to take the total kilowatts used and divide. Warning - if the power goes out, all the counters reset to zero.

Steve

Thanks for the idea, but I need an easy way for the users , mostly semi-unsupervised graduate students, who need the simplest way to keep track of the time the instruments are actually in use. I worked in a university chemistry dept for over 25 years and it's difficult to describe the inability of some so-called "bright" people to understand simple concepts outside of their very narrow area of expertise. In the old days, we used log books to keep written records of who used an instrument and the time it was turned on and off, but I estimate the data as less than 60% accurate at best.

A semi OT example: we had a spectrometer that contained a "sample compartment flood" barbed fitting so the user could displace the normal room air with nitrogen or another inert gas if the regular atmosphere would interfere with the particular wavelength of light they were using. One inexperienced user misinterpreted the word "flood" and hooked up a water line. That was only time I ever saw a field service engineer actually cry when he saw the results....:(

flylo
10-26-2011, 10:06 PM
I've used the vibration meter on several things. Look around you can get them for under $30.