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Voltage Divider (current not stable)

Voltage Divider (current not stable)

Voltage Divider (current not stable)

Hello! I recently built a voltage divider, and tested out resistors before soldering, which were in good condition. However, when I connect my divider to the HV supply my current seems to be unstable.

The current should read 210microA, but it keeps fluctuating between 218-219 even after 10 minutes of voltage running through it. I have re-tested the resistors still connected to the board with the use of a multimeter and they all still give me their correct value. I even added extra solder support to the resistors thinking that one might be lose but I have had no luck in stabilizing it.
Any suggestions?

I would greatly appreciate it,

RE: Voltage Divider (current not stable)

Can you post a drawing of your circuit including your input voltage, resistances, and readings? You haven't given enough information to figure out what is going on here.

RE: Voltage Divider (current not stable)

A fluctuating output from a voltage divider is often a strong indication that the voltage being divided is fluctuating.

"Why not the best?"
Jimmy Carter

RE: Voltage Divider (current not stable)

How high is the voltage? DC or AC? Did you use resistors rated for the voltage range? Above a several hundred volts you need to use more specially constructed resistors, to avoid internal breakdown and arc tracking in the coating materials.

What kind of construction are the resistors? I.e. carbon, metal film? Metal film and similar resistors have a lower temperature coefficient, and would be less susceptible to thermal fluctuations - which begs the next question, are the resistors exposed to air currents?

RE: Voltage Divider (current not stable)

Am I reading it right? You have a fluctuation of 1 microamp? That's a small number - what are you reading the amps with?

RE: Voltage Divider (current not stable)

First question... what leads you to believe the output should be perfectly stable at one voltage/current?

Dan - Owner

RE: Voltage Divider (current not stable)

"...should read 210microA, but it keeps fluctuating between 218-219..."

Based on some assumptions about the sort of DVOM that you're using, this is likely all perfectly normal.

The offset is probably within tolerance, including both source errors and instrument errors (both % and count).

Also, the "fluctuation" in the final digit can be as simple as the "count" (within the meter) being +/- 1 (or more).

One doesn't trust digital readouts to clearly communicate fluctuations. One switches to an oscilloscope.

RE: Voltage Divider (current not stable)

Right, thats normal, its all about the multimeter tolerance reading, if you got even more accurate multimeter it maybe not reading the 210 micro-ampere as it is and to be close to that value, but you can try more accurate

So don't worry , you're so close to the readins you need, and its the multimeter tolerance issue

I hope i helped you,regards

RE: Voltage Divider (current not stable)

If the current is around 218.6 micro Amps a very verry small fluctuation may cause the meter to jump between 218 micro Amps and 219 Micro Amps.

"Why not the best?"
Jimmy Carter

RE: Voltage Divider (current not stable)

There is a tolerance rating of 5-10% on typical carbon film resistors.

RE: Voltage Divider (current not stable)

ALL well said; plus remember that dynamic values, even in R&D Lab Quality components rarely match static values when installed in a system unless tested in the system and selected to do so.

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