# What is a device which compare a current signal and voltage signal and give me one output or two.

#### xDidan

Joined May 23, 2019
6
I would like to know if there are any device which can compare current source like 5A(alternating) with a voltage source like 1V (alternating) and give me an output. If not, which circuit I should make to have this?

#### shteii01

Joined Feb 19, 2010
4,644
Normal people compare similar items. They compare apples to apples, oranges to oranges. Current is not voltage. Voltage is not current. There is no point comparing them.

#### xDidan

Joined May 23, 2019
6
Normal people compare similar items. They compare apples to apples, oranges to oranges. Current is not voltage. Voltage is not current. There is no point comparing them.
Ok and there is a device where I compare only current sources signals? I want to measure 50A to compare with 20A, lets say. Its analog to op amp comparator for voltages, but instead voltage I wanna current.

#### shteii01

Joined Feb 19, 2010
4,644
It probably exist.
It is easier to run current through the resistor. That generates voltage across the resistor. Then you compare voltages. 1 volt is equal to 1 ampere through 1 ohm resistor. Basic physics.

#### crutschow

Joined Mar 14, 2008
31,492
If this is main's current then you will isolation, such as by using a current transformer to generate a voltage to the current, and isolate the voltage from the current.

#### shteii01

Joined Feb 19, 2010
4,644
If this is main's current then you will need isolation, such as by using a current transformer to generate a voltage to the current (the part in bold makes no sense to me), and isolate the voltage from the current.
I know it is late/early.

#### drc_567

Joined Dec 29, 2008
1,156
... A wattmeter multiplies alternating current times alternating voltage times the cosine of the phase difference angle, giving watts. However, they usually only work with a standard frequency such as 60 hertz.

#### crutschow

Joined Mar 14, 2008
31,492
I know it is late/early.
I meant to generate a voltage from the current.

#### eetech00

Joined Jun 8, 2013
3,418
If this is main's current then you will isolation, such as by using a current transformer to generate a voltage to the current, and isolate the voltage from the current.
Hi

Or you can use an "RMS to DC" converter chip that provides isolation.

eT

#### crutschow

Joined Mar 14, 2008
31,492
Hi

Or you can use an "RMS to DC" converter chip that provides isolation.
Is there such an animal?

#### Daniel Sala

Joined May 28, 2015
65
I would like to know if there are any device which can compare current source like 5A(alternating) with a voltage source like 1V (alternating) and give me an output. If not, which circuit I should make to have this?
Thinking of e.g. MOSFET VGS to IDS curves, not sure but maybe with a graph with an -X and X and a Y axis? Someone far smarter than I am could figure out how to plot that with code and any computing device from a Pi to a datalogger or similar. Would take a while to consider how to put together analog interface as I've never even considered such a circuit.

#### crutschow

Joined Mar 14, 2008
31,492