Measuring 0-150VDC as a 0-10VDC Signal

Could I do this by connecting a 1/4W 1500 ohm resistor and a 1/4W 1000 ohm resistor in series, with the 1500 ohm connected to the +DC and the 1000 ohm connected to the -DC? Would that produce a usable 0-10VDC signal between the center of the two resistors and -DC? Are there any other things that I would want to add to the circuit to keep the signal from going above 10V, like a zener diode, and how would I implement that? Should I use larger wattage resistors?

You need a ratio of 14/1 - so 14K and 1K would work - but are probably too low a value.

You can work out the required wattage using ohms law and W=VxI.

You can't go too high, because it depends on the load resistance of the metering circuit - but you haven't mentioned that?.

You are right about the 14/1, of course; I wasn't paying attention there. The metering circuit is going to be a PLC input, or an isolated 0-10V converter (to isolate the -DC if required). Neither of those should be a very big load at all, but I could figure it out with Ohm's law.

The only thing I worry about is protecting the circuit from more than +10VDC if something were to go wrong.

kittydog42 said:

You are right about the 14/1, of course; I wasn't paying attention there. The metering circuit is going to be a PLC input, or an isolated 0-10V converter (to isolate the -DC if required). Neither of those should be a very big load at all, but I could figure it out with Ohm's law.

The only thing I worry about is protecting the circuit from more than +10VDC if something were to go wrong.

Click to expand...

Yes it is a concern, if the lower value resistor was to ever go open (by itself or human error) then your measurement system to 'see' the high undivided voltage. A downstream zener might give you some insurance protection but it's value would have to be such as not to effect the normal measurement range but still protect the system from it's max safe input voltage.