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| Water Heater Monitoring |
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| sparky961:
--- Quote from: Stuart on January 06, 2015, 11:09:01 AM ---Excuse the safety warning but be extremely careful with CT,s The short is the same as the meter and no harm will come to the CT Reason they are capable of producing a high voltage on the output terminals --- End quote --- Thanks, I did see that when doing some preliminary research. You've reminded me of the importance. |
| sparky961:
--- Quote from: awemawson on January 06, 2015, 11:20:04 AM ---He is measuring current, which he has previously related to power at 110 at 12.2 watts per milliamp. So measuring the heater running off 240 his 1 mA reading is now (240 / 110) * 12.2 or 26.62 watts per milliamp. So 102.8 mA represents 2.7 kW Again probably within the measurement accuracy :clap: --- End quote --- I did notice that on different DVOM ranges that the reading changed fairly significantly (10's of mA). My assumption (that bad word again) was that it had to do with the meter's internal resistance so I thought I could negate that effect by using that range for all my measurements. Do you think I could improve accuracy by using an external resistance in the CT loop? It did nag at me a bit that the measurement was inconsistent on those different ranges. I suppose the way to answer the question is by collecting more data from known sources. |
| vtsteam:
Sparky, all theories about why, and projections from them aside, as I said earlier, you can simply characterize your meter by a few more data points, and that's all that is really needed. 1.) do a reading for a 200 watt bulb (or so) 2.) do a reading for the water tank with both elements on (probably when it is run out of hot water completly) That will allow you to do a graph of 5 points instead of 3. Much more meaningful. Then we can see what's going on rather than guess what's going on. |
| vtsteam:
And yes, you are depending on meter resistance, which is itself variable, not fixed. It's usually reckoned in ohms per volt. But this is again just one more possible theory, not a replacement for data, which would show you what is going on before attempting to explain why it is going on, So forget about meter resistance. Get the data first, and then you will likely find the answer out of all the theories, because it will point to one or the other. The curve(s) will suggest the answer. |
| lordedmond:
I am getting confused here not an unusual thing Are we talking about measuring AC current still The term ohms per volt refers to the meter when used in volts , current is measured by referencing the volt drop across a shunt ,which is very low and the meter resistance will have very little impact being in parallel with the said shunt As to using lamps are they 100 watt ? Have you proved that because it seems like they are being used as a standard If you want to be sure get a clamp on amp meter and a decent volt meter and go from there , then if you need to remotely measure use the figure produced to calibrate you gizmo Normal V I calc will be ok as we are dealing with a resitive load and power factor is unity so has no effect on the result Stuart |
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