AC current sensor with interface

Look at:

On 5/20/2010 9:33 AM Bennett Price spake thus:

Hmmm; only $255 ...

Not a sensor, but whatever ...

How 'bout an inexpensive current xformer, which seems to be what the OP wants?

There's three obvious branches: you can go the full industrial- automation route (with DIN racks, enclosures, modules) - about $100-300 per module, and they'll talk RS-485 or Ethernet, or....

You can go the flexible-but-crufty route, and use any old ammeters, with a video camera aimed at them. The computer just captures some images, at the end of the day you can review it all.

The slickest solution, though, is to park a data logger (small battery-powered recording meter) at the appliance, and occasionally download its contents by walking over and plugging it into your laptop.

Den 20.05.2010 19:38, skrev David Nebenzahl:

I need a *digital* interface which can be read / monitored by a computer.

The Coleparmer module does the trick, but it just goes to max 25A and I hoped such modules would be less expensive than those...

Other comments?

rgds

Geir

You don't say exactly what you're trying to accomplish, so this may be tangent to your requirements....but I'll try not to let that stop me.

I set out to instrument my home for the purpose of energy conservation. I intended to use a current probe and PIC processor to acquire the current data and send it via RS232 either directly or via RS232-Bluetooth adapter.

I started with Mike's metrology rule #1: Never ask a question unless the answer will modify your future behavior.

And a corollary: Real-time data without real-time control is overkill. All it gives you is worry.

I went around the house with a RMS power meter measuring everything that would unplug. The bad news is that a bunch of things like a wireless telephone at 5W each really add up. The worse news is that I'm unwilling to give them up. I did unplug infrequently used vampire devices.

Since most things are either on or off. If you know the consumption, you don't have to measure it in real-time.

A Kill-A-Watt device for under $20 will measure and log data for you. But you have to interrupt the circuit.

Moving on to the harder devices, I started with the biggest energy consumers.

First stop was the furnace. It's gas. Hmmm. I determined from watching the gas meter go around that the 60KBTU/HR rating was pretty accurate. So, it was sufficient to measure the on-time. For that, I used a hunk of cardboard on a microswitch that opens when the furnace fan comes on placed over a vent. I used an old Palm III to plot the on-time. Calculate the gas cost plus the fan cost determined using a hand-held current clamp meter completes the calculation.

For most things, they're either on or off. If you use 'em less, you save. Knowing exaclty how much you're saving TODAY isn't useful. If your furnace thermostat is already as low as you can tolerate, you've done all you can. And you didn't need a single measurement to reach that conclusion.

Next, I tackled the electric water heater. The wires are accessible, so I used a clamp-on probe from an old Triplett analog meter. It's much better than more modern sensors because it puts out 500mV/Amp. Plugged that into a Radio-shack DVM with RS232 output and used a laptop to log the result. Now, I know how much it costs to take a hot shower or wash a load of clothes. The thermostat is already as low as I can tolerate. Not much use for additional measurements. The plan to use a PIC to measure the sensor output and transmit it via RS232 or bluetooth has been aborted.

Kitchen appliances weren't worth measuring. I'm not gonna stop reheating my coffee just because I have real-time data on the microwave. See Rule #1 above. I did buy an energy-efficient fridge.

The air conditioner wiring wasn't accessible, so I took an alternative approach. Our neighborhood just got those newfangled digital power meters from the power company. Mine puts out an infrared pulse for every watt-hour consumed.

WalMart sells individual cake slices in a plastic box that is a nice friction-fit over the power meter cylinder. It's just the right size to put in a PDA. The handspring visor variant of the Palm III works better because the IR sensor is on the side.

A little bit of code and a lot of hair-pulling later, I have a program that graphs and logs power consumption. And since it measures exactly what the power company charges for, I don't have to worry about power factor, etc.

If you control what else comes on at the same time, you can determine the "signature" of various major power consumers. That done, you can usually tell what's going on/off from the log.

The PDA cake-boxed onto the power meter can do anything I need to monitor electricity consumption.

Now that I have the data and have modified my behavior, the measurements stuff in in a drawer. Refinement plans have been aborted. I'm really glad I didn't invest a lot of $$$ in permanent measurement and control facilities.

Rule #1 rules...

YMMV.