Normalizing 1 Meg ohm DVM meter plug

[Vanclair]

At work we use these 1 Meg ohm Normalizing Black box with banana plugs that goes to the DVM meters inputs RED and BLACK probes

What are these Normalizing boxes do for DVM meters? it puts a 1 meg ohm resistor across the DVM meter probes for measuring voltage

It's to make a normalizing circuit , which is a voltage divider it looks like

But when do you use these normalizing circuits to do voltage measurements?

 

[betwixt]

This is not standard equipment. It is either there to present a 1M resistance across the probes at all times, regardless of the DVM itself or it is a potential divider to drop the voltage being measured so it lies within the DVM measurment range. A clue would be in the DVM range you use, for example, if you set the DVM to read 1V and apply 1V across the probes, does it say 1V or something smaller, for example 0.1V would indicate a divide by 10 network was inside the plug.

Brian.

 

[Vanclair]

It is either there to present a 1M resistance across the probes at all times

Yes, plus a resistor decade box in series to get a 10volts dc reference

We use the 1 meg ohm Normalizing plug which goes across in parallel in the DVM meter input jacks, then we use a resistor decade box in series , we rotate the resistors decade box until the DVM meter reads 10 volts DC. This is called a Normalizing circuit

I'm not sure what this normalizing circuit is or why it is used to take certain measurements

 

[betwixt]

I'm guessing it's purpose is to set a maximum resistance across the DVM jacks. The decade box is the series resistor in a potential divider and the 1M becomes the parallel resistance. Without it, the resistance at the input of the DVM might be so high that the decade box couldn't provide enough series resitance.

Brian.

 

[FvM]

Most DVM have 10 Mohm input resistance. Connecting 1 MOhm in parallel creates an odd resistance value, so I'm absolutely not sure about the purpose. May be the resistance value is different.

By the way, have you been here before? Your style of asking questions sounds familiar.

 

[betwixt]

FvM, from the sound of it, the actual value isn't important as long as they can achieve the desired attenuation by adjusting the decade box. I suppose to work with a standard 10M input resistance the decade box would need some pretty high values in it!

Brian.

 

[Vanclair]

Here is the pictures

What does this circuit do? it's to change the DVM meters input impedance?

 

[betwixt]

I can't read the thumbnail pictures and the full sized ones are too large for me to download but it looks like it just goes across the DVM input so the connections to the terminals see close to 1M regardless of the input impedance of the DVM itself. So it's purpose is:
1. ensure the DVM appears to be no more than 1M impedance
2. allow reasonable resistor values to be used in an attenuating circuit.

You can imagine the problem if the DVM had say a 20M input impedance, the values in the decade box may have to be in the hundreds or thousands of Megohms range.

Brian.

 

[dextermccoy]

I don't understand the theory or why would want to "normalize the meter readings?

What circuits or tests would you want to normalize the meter readings?


Do you now understand the concept of "normalizing?"
No I don't, please explain to me what it is and what it is used for please?

When have you used to "normalize" the DVM meter readings?

What circuits or tests would you want to normalize the DVM meter readings?

Without normalizing the DVM meter readings what would happen? the readings would be to hard to make sense?

- - - Updated - - -

1. ensure the DVM appears to be no more than 1M impedance
2. allow reasonable resistor values to be used in an attenuating circuit.

But why would they want to use a 1M impedance across the DVM meter terminal at all times?

it looks like it just goes across the DVM input so the connections to the terminals see close to 1M regardless of the input impedance of the DVM itself.

Yes true it does, but why?

What type of test is this doing?

If I remove the normalizing circuit, what would happen? the DVM meter reading is normalized, without it being normalized the DVM meter would be what?

 

[betwixt]

I don't think it is to normalize the readings, it's to normalize the DVM impedance so it will work with the decade box.
Inside a decade box is a switched bank of resistors with values in x1, x10, x100 and so on Ohms. When in series with the DVM they are the 'top' end of a potential divider and the DVM impedance is the 'bottom' (ground) end. I think the 1M resistor is to lessen the effect of the DVMs own input impedance by setting a maximum value it can ever appear to be. Without it the decade box might have less effect and the voltages might read higher than intended.


Brian.