I have a current transformer measuring current going to my hot water service. The output of the current sensor is an AC voltage that I measure 500 times a second and calculate RMS of in software. This works quite well but I would like to just measure a DC voltage once every 10 seconds. I tried converting the AC voltage to DC using 4 diodes but the signal is below 0.6V so I got absolutely nothing. Any better way to do this?

 

4 diodes won't give you a DC voltage. Why do you think it will? What did you use to measure the voltage?

 

If the current sensor is a current transformer you can use a bridge rectifier but it must be between the transformer and the "burden" resistor. Of course what you will get will be pulsing DC which you can filter with a capacitor, but then the result will be average current (or peak), not RMS. Since a heater is a resistive load, the ratios of peak, average and RMS are well defined, assuming there is nothing doing anything like phase angle control or rapid on-off switching.

 

If the current sensor is a current transformer you can use a bridge rectifier but it must be between the transformer and the "burden" resistor. Of course what you will get will be pulsing DC which you can filter with a capacitor, but then the result will be average current (or peak), not RMS. Since a heater is a resistive load, the ratios of peak, average and RMS are well defined, assuming there is nothing doing anything like phase angle control or rapid on-off switching.

Thanks, that makes sense. Because it outputs a current it will increase the voltage to compensate for the diodes. I just need to work out if I can get to the resistor as it is integrated.

 

I neglected the fact that the burden resistor value is normally very low, which may make simple filtering a problem. Especially in view of the fact that the burden resistor is integrated, you might be better off to use an op-amp precision rectifier circuit.

 

If you increase the impedance into which the current transformer output is fed, the resultant voltage will be increased. You can then use diodes to rectify the voltage, giving a readable value.

Based on my experience of doing this, the impedance need only be a few tens of ohms.