I am happy with the temperature sensors, basement, first floor and second floor. wild difference at any time.
but now I want to monitor the oil burner. I am thinking a CT on the furnace. the blower is about 7 amps and the oil burner is about 2 amps.
the CT into an op-amp, into the ADC and I should be able to monitor the differences in operation.
I could put on two sensors, just to see if there is power, but the CT offers that slight bit on separation.
first question is if I am on the right path.
looking for others who have tried this was not fruitful. other seemed to have asked, but no posted results.
Hi Dave,
"Dave , I don't think you have the grounds connected..." (2001 space odyssey)
We meet again. Would it be asking to much to get some electrical specs ? (what kind of heater ? 120VAC powered oil filled or space?)
blower is on the same power to the furnace, but on separate internal controls.
The oil burner atomizes the fuel that then burns.
the blower circulates air through the heat exchanger.
the thermostat calls for heat, the oil burner starts and spews flames into the heat exchanger.
during this time, fuel is being used at X gallons per minute. once the heat exchange reached temperature, the fan thermostat energizes the forced air blower for the hot air. this operates independently from the oil burner. The oil burner may shut off once the heat exchanger reaches it's upper limit, the blower will continue to run because the heat exchanger is over temp.
As the heat exchanger cools, and the thermostat is still calling for heat, the oil burner will come on again. The blower will continue to run. once the heat exchange cools off the blower will stop.
I am mostly interested in the hours that that the oil burner is running. but, since I am already into the unit, I would like to also see the fan operation.
my first options seem to be monitor the voltage to the fan and to the oil burner. voltage is present, the unit should be operating.
the CT seems to be a one stop shop. Low power = burner only. High power = both blower and burner. medium high = blower only.
sounds like a two stage op-amp. first stage get the DC following the input. second stage for amplification and a simple RC filter to smooth out the output.
not enough forward voltage for a diode to rectify the AC.
That is most likely at 100 amperes rms AC current though the CT core, but as the rest of the notes explain, the burden resistor converts the current into a voltage that the Arduino can easily measure. That CT is overkill for your application but you are on the right track.
Most CTs suitable for lower current AC measurements put out quite a bit less current, so you are dealing with a few mV/ampere (after conversion by the burden resistor). Some years ago I used a single stage precision rectifier op amp circuit and a CT to monitor hot tub current. It converts peak current into a DC voltage and worked extremely well. Some discussion can be found on the Spark Fun forum here: Convert AC voltage from current transformer to DC voltage - SparkFun Electronics Forum
BTW you can get free samples of CTs from Coilcraft.
Jremington,
You must know a lot about op amps. I was wondering if you could answer a couple of question for me. Attached are the datasheets for the Burr-Brown INA169 , the Sparkfun INA169 Breakout, a worked example of a differtial amplifier op amp circuit and an equivilent schematic of the Max4172 High Side Current Shunt Monitor
So I've worked with many op amp circuits but never any thing like these shunt monitors and I am a little puzzled by the transistor that is apparently part of the current mirror , which if I understand it correctly , basically multiplies the current of the input resistor by some large amount (like 50) ,yielding an output that can be measured by an A/D. The only other op amp circuit I have seen with a transistor is a logarithmic op amp where the transistor is the feedback element, but the shunt monitor is different. It' s a like a special purpose differential amplifier. So my question is what is that transistor doing and why is it there ?
Do you mean Q1 in that diagram, or the current mirror itself? Q1 is simply controlled by the op-amp such that with whatever voltage is on its collector, it draws enough current to balance the differential input. It is doing exactly the same as a feedback resistor does when fed with a voltage from the op-amp output, except that it generates a current (and feeds it to the external circuit via the proportional current mirror) instead of a voltage.
Linearity/ logarithmicity is not the point, it's just feedback.
So the transistor works such that is draws current away from the V+ input of the op amp driven by the fact that the V+ pin is more positively biased than the V- pin. Thank you for the answer.
