# Inquiry, how to measure the amount of voltage, current, and resistance this device

#### Most Wish

Joined Mar 21, 2024
5
Hello!

I just want to ask how to measure the amount of voltage, current, and resistance in this device using an analog multimeter.
like I want to know the polarities of the probes, where to connect them, if they are connected in series or in parallel, and if the device should be turned ON or OFF.

#### dl324

Joined Mar 30, 2015
17,017
Welcome to AAC!
I just want to ask how to measure the amount of voltage, current, and resistance in this device using an analog multimeter.
like I want to know the polarities of the probes, where to connect them, if they are connected in series or in parallel, and if the device should be turned ON or OFF.
Is this schoolwork or a testt?

#### Most Wish

Joined Mar 21, 2024
5
Welcome to AAC!
Is this schoolwork or a testt?
No, I am a newbie, and I just found this device in my father's storage room.

#### Most Wish

Joined Mar 21, 2024
5
Welcome to AAC!
Is this schoolwork or a testt?
I wanted to learn about electronics and stuff, since I am an incoming 11th grade

#### dl324

Joined Mar 30, 2015
17,017
No, I am a newbie, and I just found this device in my father's storage room.
I don't see a rectifying diode in the circuit, but test points D and J are labeled ground, so you'd put the negative lead from the analog meter there for all of the measurements except for R and the LED. For those components, you'd put the negative lead on F and H, respectively.

I don't see any provisions for measuring current directly, so you'll have to use resistor values (are they given anywhere?) to calculate currents in each loop using Ohm's Law.

Could you post a picture of the test box from the top so we can see what's marked around the rotary switch?

EDIT: When you measure the resistor values, make sure there is no power applied to the box. You can't usually measure resistances in-circuit, but you can on that box with the switch opened. The capacitor will have to charge to be able to measure RL, so wait until the reading settles.

When using an analog meter, you set the range to the highest and go to lower settings as required. This will avoid "pegging" the needle which can damage the movement.

Also note that analog meters need a battery to measure resistance. Take care if you measure currents (which I don't usually do) because those old analog meters didn't always have fuses. I blew a resistor in my old RCA meter when I was a newbie.

Last edited:

#### MrAl

Joined Jun 17, 2014
11,587
Hello!

I just want to ask how to measure the amount of voltage, current, and resistance in this device using an analog multimeter.
like I want to know the polarities of the probes, where to connect them, if they are connected in series or in parallel, and if the device should be turned ON or OFF.

Thank you for your responses!!View attachment 318064View attachment 318065
Hi,

I see a line cord. You have to be very careful using that, as it could easily overpower the device and cause a fire or even explosion.

You would have to find out what voltage should be applied to the input, which could be 12 volts AC for example. That would mean you need a transformer too.
We don't yet know what the rotary switch does because we can't see the markings.

#### Most Wish

Joined Mar 21, 2024
5
I don't see a rectifying diode in the circuit, but test points D and J are labeled ground, so you'd put the negative lead from the analog meter there for all of the measurements except for R and the LED. For those components, you'd put the negative lead on F and H, respectively.

I don't see any provisions for measuring current directly, so you'll have to use resistor values (are they given anywhere?) to calculate currents in each loop using Ohm's Law.

Could you post a picture of the test box from the top so we can see what's marked around the rotary switch?

EDIT: When you measure the resistor values, make sure there is no power applied to the box. You can't usually measure resistances in-circuit, but you can on that box with the switch opened. The capacitor will have to charge to be able to measure RL, so wait until the reading settles.

When using an analog meter, you set the range to the highest and go to lower settings as required. This will avoid "pegging" the needle which can damage the movement.

Also note that analog meters need a battery to measure resistance. Take care if you measure currents (which I don't usually do) because those old analog meters didn't always have fuses. I blew a resistor in my old RCA meter when I was a newbie.
it is marked "SET"and there's number surrounding that switch labelled from 1 to 5.

#### Most Wish

Joined Mar 21, 2024
5
I don't see a rectifying diode in the circuit, but test points D and J are labeled ground, so you'd put the negative lead from the analog meter there for all of the measurements except for R and the LED. For those components, you'd put the negative lead on F and H, respectively.

I don't see any provisions for measuring current directly, so you'll have to use resistor values (are they given anywhere?) to calculate currents in each loop using Ohm's Law.

Could you post a picture of the test box from the top so we can see what's marked around the rotary switch?

EDIT: When you measure the resistor values, make sure there is no power applied to the box. You can't usually measure resistances in-circuit, but you can on that box with the switch opened. The capacitor will have to charge to be able to measure RL, so wait until the reading settles.

When using an analog meter, you set the range to the highest and go to lower settings as required. This will avoid "pegging" the needle which can damage the movement.

Also note that analog meters need a battery to measure resistance. Take care if you measure currents (which I don't usually do) because those old analog meters didn't always have fuses. I blew a resistor in my old RCA meter when I was a newbie.
I think you can insert resistors on those blank parts that are labelled "R".

#### ericgibbs

Joined Jan 29, 2010
19,024
Hi MW,
Did your Father work for a telephone company?
E

#### dl324

Joined Mar 30, 2015
17,017
I think you can insert resistors on those blank parts that are labelled "R".
You can end the need to speculate by opening the box.

#### MrAl

Joined Jun 17, 2014
11,587
I think you can insert resistors on those blank parts that are labelled "R".
Hi,

That was one of my thoughts also, but I did not mention it because those jack holes could be for inserting banana plugs for the purpose of making measurements.
So it could be you insert parts or you insert meter leads. The switch could be for setting different values that are already inside.
Unfortunately these are all just guesses until you stick a meter in the two holes labeled "R" and measure the resistance. You can also measure the RL position. That would tell us a lot more, however this box looks like a one-off design for some special purpose.

#### MrChips

Joined Oct 2, 2009
30,986
You don’t need this for your studies. Put it back where you found it.