Hi all,
I have an Emontx3 which is working correctly except input 2 is suddenly giving very low readings. All others are correct. I have transferred the CT to another input where it gives the correct readings suggesting a problem with input 2. Are there any other troubleshooting steps I can take before replacing the board which dates back to April 2014?
Re: Emontx3 input showing incorrect readings
If you have a programmer, it's probably worth reloading the sketch. If it's still the same, you could try Robin's Mk2 Code variants and associated tools: http://openenergymonitor.org/emon/node/1757 - both MinAndMaxValues and RawSamplesTool_4ss_2 should be useful - you're looking for a signal centred on 512 or thereabouts.
Other than checking that you have approx 1.65 V dc at the CT input (that's the '512' above), there's probably little you can do unless you have access to an oscilloscope and can check that you have the correct voltage at the analogue input of the processor - you should see 11 mV rms (31 mV p-p) per amp of current, sitting at 1.65 V above ground.
Re: Emontx3 input showing incorrect readings
Hi
I'm having a similar problem. Using the same CT, values are incorrect on CT1 and CT3 and correct on CT2.
I'm using the AC/AC power source
Re: Emontx3 input showing incorrect readings
Webby hasn't come back with any more information, so I think you need to tell me which exact version of emonTx you have, which sketch you are using and exactly how you are measuring and recording the values. Do you have a programmer, and if so, can you try the test sketches I mentioned above?
Re: Emontx3 input showing incorrect readings
I have an EmonTVv3.4 without any radio (using ftdi adapter)
I'm measuring a transformer consumption using a SCT-013-000 clam and comparing to the values of a comercial power metering plug. The plug measures 11W.
I'm using emonTxV3_4_DiscreteSampling from github.
Re: Emontx3 input showing incorrect readings
At 11 W, you really must not expect an accurate reading - that is around 0.05% of the maximum possible reading. If you use a load that is even 1% of maximum, you should get a much better match.
Think of it this way: 11 W = 46 mA primary current in your CT, the secondary current should be 23 μA, giving a peak-peak voltage of 1.4 mV at the ADC input. One ADC sample is 3.3/1024 ≈ 3.3 mV wide. Therefore your input is less than the resolution of the ADC.
Also, even though you're using the same CT, bear in mind that the CT's data sheet states: "Non-linearity ±3% (10%—120% of rated input current)", so even the CT's accuracy is anyone's guess, at that current.
Re: Emontx3 input showing incorrect readings
You are right, moved to metering an dehumidifier (300W) and values show up correctly (+/- 10w).
I just got confused because the value in the CT2 was actually right :)
Thx Robert!
Re: Emontx3 input showing incorrect readings
"the value in the CT2 was actually right"
At the current you had, that was pure luck.