I've got a SCT-013-00 CT clipped around 1 of the wires to a 2400W resistive heater. It's plugged into CT1 jack of an emonTX running the sample script for current only. Following some troubleshooting tips I read elsewhere in this forum, I measured 1.4VDC at both ends of the burden resistor, and I also confirmed that the CT plug is making contact in the jack because the resistance across the PCB contacts goes down from 19 to 16 ohms when the CT plug is inserted (CT measures 104 ohms unplugged). My script is displaying values like this, regardless of whether the CT is connected, and regardless of load:
39.91 0.17
40.35 0.18
40.35 0.18
40.33 0.18
39.17 0.17
40.15 0.17
40.58 0.18
39.60 0.17
40.85 0.18
I understand spurious low readings can come from noise, but I was hoping to see some higher readings than this with the heater running!
Any other troubleshooting checks I can do? Unfortunately I don't have any meter that can read AC millivolts.
Cheers,
Ben (Australia; 230V/50Hz)
Re: emonTx troubleshooting
Are you using the current (downloaded after mid-October) EmonLib? There was a fault in that which gave low readings.
Assuming you have disabled CT2 & CT3, you should be seeing the supply voltage (x 100) as the second number, e.g 3300 meaning 3.3 V. As you're not seeing that, it means the supply voltage is not being read correctly.
If line 219 of EmonLib.cpp does not have the bit in bold #if defined(__AVR_ATmega168__) || defined(__AVR_ATmega328__) || defined (__AVR_ATmega328P__) at the end, you've got the old library.
Re: emonTx troubleshooting
Thanks Robert. Yes, EmonLib.cpp does contain that bit in bold.
The numbers in my original posting actually came from this example script bundled with Emonlib-master:
// EmonLibrary examples openenergymonitor.org, Licence GNU GPL V3 #include "EmonLib.h" // Include Emon Library EnergyMonitor emon1; // Create an instance void setup() { Serial.begin(9600); emon1.current(1, 111.1); // Current: input pin, calibration. } void loop() { double Irms = emon1.calcIrms(1480); // Calculate Irms only Serial.print(Irms*230.0); // Apparent power Serial.print(" "); Serial.println(Irms); // Irms }But I'm now trying EmonTx_123 that came with emonTxFirmware-master, and having better luck! Here are the results:
22 3293
26 3293
29 3293
23 3293
24 3293
2209 3293 << heater switched on for these next several readings
2227 3293
2222 3293
2208 3293
2222 3293
56 3293
28 3293
27 3293
28 3293
30 3293
21 3293
29 3293
31 3293
29 3293
Next I'll get an ampmeter and do some comparing. Any further advice on how to eliminate the false readings on no load?
Cheers, Ben
Re: emonTx troubleshooting
Your 30 W or so readings are down to noise or pickup - quite possibly at least partly from the digital circuits inside the processor itself. They are quite normal, though admittedly undesirable. What it amounts to is if the midpoint bias voltage just happens to sit right on the boundary between two values of the A-D converter, the slightest whiff of noise will flip it between values and this will be the same as a current that swings the 2 counts peak-peak. The mechanism is explained a bit more fully here. Trystan did some wonderful animated pages a few months ago demonstrating how the errors vary here, here and here, as well as this. And these deal purely with theoretical errors - in the real world you need to factor in noise and pickup as I've already mentioned.
I didn't realise which sketch you were using (and you didn't say!) so the first lot of readings you quoted were actually Power (assuming 230 V supply) and rms current. You'll be pleased to know your problem wasn't you! The example had apparent acquired an editing error when the library was updated, you were actually trying to read the wrong input. I've emailed Glyn & Trystan so they'll put it right soon.
The latest sketch displays what I originally thought, and assumes a system voltage of 240 V, if yours is not that, you need to change it to correctly estimate the "power " (actually, it is VA - apparent power).