OK, we will look at a few pictures of what I am getting at here, therefore three images are attached for your viewing pleasure.
However, first we can take a look at a choice of comparator. You may want to
give this link a read. For a simple single comparator I would lean towards the LM311 which is covered in the link. Also
here is the data sheet.
The first image is that of an everyday CT (Current Transformer) compliments of my kitchen table. Lets assume (since you can't see otherwise) that it is a 1,000:5 CT. Therefore 0 to 1,000 amps = 0 to 5 amps. I am sure you have a handle on that.
The next device pictured is a nice current transducer very similar to the CT but this device is a 0 to 20 amp device that provides a DC output. There were some such devices linked to earlier in the thread. These current transducers are powered in a 24 VDC current loop where full scale out is 20 mA or in this case 0 to 20 amps = 4 to 20 mA (4-20 being a very popular current loop).
The third picture shows the actual configuration of the two devices. Now something to consider here is that current transformers and current transducers (both our devices) measure current based on amp turns. Now the output from our first CT is 0 to 5 amps, so what I have done on the current transformer, remember the range is 0 to 20 amps is wrap four turns of the primary CT secondary through the second current transducer secondary.
So what we now have3 in our images is 0 to 1000 amps = 0 to 5 amps = 4 to 20 mA in a nice clean DC signal with a good accuracy ratio.
I should point out that the current transducer pictured has a 4 - 20 mA output, however, they can be had with a voltage output. This is simpler and better to drive a comparator circuit. I pictured what I had lying around.
So I take my 4 to 20 mA and run it through a nice precision small 250Ω or 500Ω resistor and get 0 to 1000 amps = either 1 to 5 volts or 2 to 10 volts. Everything is scaled very nice and actually very accurate. I would venture an overall uncertainty of +/- 10 amps at 1000 amps.
Now we get to the comparator. We use a 24 Volt DC small power supply to power our second current transducer for the current loop. We also take that 24 VDC and run it into a simple 12 volt regulator like a LM7812 and use that 12 volts out to power our comparator circuit. The LM7812 will give pretty good regulation so we use maybe a 10 KΩ pot to set our comparator reference.
I should point out that the second device does have terminals on the top above the +/- signs.
Does this help?
Ron