monitor outlet power consumption

[cactusman]

I'm interested in monitoring power consumption at specific outlets in a facility using Labview and NI DAQ systems. Essentially what I'd like to do would be to use one specific outlet as a monitoring point for all the rest of the outlets in a facility or connected to that circuit. I'd like to be able to create a network map of the outlets to be monitored by sending some sort of signal back to the monitoring DAQ so I can label each outlet specifically and then keep monitoring it continuously to see how much power is being consumed at that outlet. Any suggestions on how I can approach this problem or if this is feasible? Thanks!

[johnsold]

Cactusman,

Watch out for the sharp spines on your cactus.

Your description is not completely clear, but it sounds as though you have two separate issues: 1.  How to measure the power at an outlet.  And 2. How to communicate the results of the measurements to a central point.

For part 1 you need to connect a wattmeter or voltage and current transducers between the outlet and the load.  The power distribution network in most facilities is a parallel voltage supply.  Thus knowing the power or current drawn at one outlet provides no information about the power or current supplied by any other outlet.  So you will need measurement equipment at each outlet to be monitored.  Do you need power, power factor, crest factor, energy, or other measurements?  What level of accuracy?  How often do you need updates?

For part 2 the method will depend on the nature of your power distribution network, the types of equipment using the power, the distances, the rate at which the data must be collected and other factors.  Communications over the power line itself is feasible, but not necessarily easy.  Safety, noise, bandwidth, and other factors must be considered.  Wireless networks (Wi-Fi for example) are becoming more popular for such applications.

If you can tell us more about your specific application, perhaps someone can make some suggestions.

Lynn 

[cactusman]

Lynn,

Thanks for the help. I'll do my best to clarify.

My hope was that if I could create a type of network diagram or circuit map for a facility, or even simpler than that, for a room in a facility, that I coud monitor power consumption at any of the outlets from one single outlet. The basic data I'd like initially would be energy consumption/kWh data for what is consumed at that specific outlet. The accuracy can be just down to the .1 kWh and I'd like to be able to view the data at something like 5 minute intervals, maybe down to the minute.

A simple hypothetical exaple of what I'd want to do would be to take a room in a lab. Lets say I've got a DAQ hooked up to one outlet for monitoring. On the other side of the lab a cooler is plugged into another outlet. I'd like to measure the consumption or energy usage of that cooler at the monitoring outlet without having to add any equipment to where the cooler is plugged in, like a wattmeter. I thought this might be possible by using sending some type of signal from the cooler outlet to initially "map" the circuit (ie some type of AM signal on top of the power signal). But then I didn't know if it would be possible to keep monitoring that outlet and others with other equipment attached to them just from my monitoring point and without wattmeters, etc.

It sounds like you're saying this is not possible. So if I had to have something plugged into each outlet I wanted to monitor what could I use for a room that is simplest and cheapest? Any further info is helpful and I'll keep trying to clarify, I've done a lot of DAQ work before but not really much involving monitoring power like this. Thanks!

[smercurio_fc]

There is a distinction between the measuring of the power consumption and the monitoring of power consumption. As Lynn pointed out, the measuring part has to be done at each point. How you do this depends on what you've got available, what you will tolerate, and what your budget is. The monitoring part is getting the information to a central location. Wireless is the easiest solution, but since you are in a lab environment you will need to evaluate any potential interference you may get from all the equipment that's there.

For measuring, I would suggest using Google to search for power consumption measuring devices. There's lots of them out there, and many come with a computer interface.  For monitoring, this is going to be dependent on what kind of device you get for measuring. 

You can also start here: Electrical Power Quality, Consumption, and Distribution Monitoring.

[johnsold]

Cactusman,

What you described is not possible.  You need to have some kind of measuring apparatus at each outlet.

Since some of your loads are things like coolers, which often have low power factors,  you cannot get a good measurement of the energy by just monitoring the current and multiplying by the voltage.  This means you need to make simultaneous, phase sensitive measurements of the voltage and or use a wattmeter/power transducer plus accumulation of the data to get kWh.

0.1 kWh in 5 minutes is 1200 W.  If this is the limit of your sensitivity, you will miss much of the energy used by low power devices.

I have not priced power transducers lately, but I would guess that you are looking at ~$100-1000 (US) per outlet by the time you get a transducer and communications to your computer.  If there was a simple and cheap way to do this, many companies would be doing it to minimize their utility bills.

Lynn 

[cactusman]

Thanks for both of you replies.

Yes, it seems that my hope of being able to both measure and monitor from a central point is not going to come true. With that in mind, I'd still appreciate any advice you might have on the best way to measure in the ways I've described at the source and then to get that data back to the DAQ. I'd really like to do this wirelessly but again this makes it more expensive. Any further thoughts are appreciated. Thanks!