Miniature Hour Meter

[davekuch]

We have just released a new product that has a component on it that we expect will be consumable and burn out after a period of time. It's a nichrome wire that we are controlling by phase angle firing a 120VAC supply to it.

For warranty purposes, my sales department has asked me to find a miniature device that we could wire into the circuit to monitor how long the device has been run. Ideally, any device would be about the size of a thumb and be able to be wired in series with the nichrome wire.

Unlike most hourmeter applications, I don't care about digit size, being able to read in direct sunlight, etc. For this application, it's all about the size!

Thanks in advance.

 

[VEBill]

I recall that there used to be a device about the size and shape of a 3AG fuse that plated the core to keep track of time. I haven't seen it for about 20 or 25 years. I'll see if I can find a reference...

These days, a tiny uC with non-volitile memory might be the cheapest solution. Obviously you'd monitor the control signal, not the AC.

 

[VEBill]

Here is a link to an image of something similar to what I recall. But the version I recall was simpler, less frills (LOL).

http://eolsurplus.com/images/UnknownHourMeter.jpg

 

[davekuch]

Thanks VE1BLL. I'll start looking for something like that!

 

[Skogsgurra]

That one cannot be wired in series with your load since it is DC operated and with a tiny current. You need to use a diode and a series resistor. Then it will work fine.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jimkirk]

Look for "micro-mercury coulombmeter" if they're still made.

Used to be popular monitoring the stylus life of phonograph turntables.

Typically used to read several thousand hours. They operate off of low voltage DC, so you'd wire it in parallel to your heating element, with an appropriate diode to convert to DC and circuit to limit the voltage to something like 5 volts, or whatever the MMCM wants.

Obviously, they have mercury in them, so may be on some banned list. Perhaps there's an equivalent made of some safer alloy.

 

[jraef]

L-3 makes some little sub-miniature ETMs that either mount to a surface and have a display, or they have PCB mount versions that store the data for reading by something with more intelligence. But as they are MIL-spec, expect that they are not cheap.

http://www.l-3com.com/products-services/docoutput.aspx?id=701

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