Re: Digital meter feedback?


Ken C wrote:
On 26 Mar 2006 17:06:53 -0800, "Chris" <cfoley1064@xxxxxxxxx> wrote:
Your vendor is deserving of negative feedback if he told you a
7107-based Digital Panel Meter (DPM) can handle what's called
"high-side measurements". He didn't know what he was talking about.
Actually, it's only because of your caution and using a current-limited
supply that your DPM is even working.

How is this meter supposed to be used?

I am measuring current in zip cord, and I do have available the
negative wire, one side of which runs to system ground (a lead-acid
battery negative terminal).

However, when I tried the meter on the black wire in this way, it
showed "-00.4" amps with no current imposed on the shunt and supply
current to the meter limited to 0.040 amps. So just using it on the
ground wire, and having one side of the shunt and the 5V negative
commoned did not work properly.

Ken C

Hi, Ken. Most of these 7107-based meters are supposed to be hooked up
like this (view in fixed font or M$ Notepad):

|
| .-----------. V
| | | |
| +5V | |In+ | |
| o-----o o-------------o |
| | | | | Current
| | | | |
| | | .-. |
| | | 1 milli- | | |
| | DPM | ohm | | |
| | | shunt '-' |
| | | | V
| | | |
| 0V | |In- |
| o-----o o-------------o
| | | |
| | | |
| '-----------' V
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

There's separate connections for power and the measurement. The 5V
supply on the left is supposed to be isolated from the voltage
measurement across the shunt on the right.

The way I was reading your post, I thought you might be doing this:

|
| +12V TOTALLY WRONG -- DO NOT DO THIS!
| o-------------------------------.
| |
| .-----------. |
| | | |
| +5V | |In+ | |
| o-----o o-------------o |
| | | | | Current
| | | | |
| | | .-. |
| | | 1 milli- | | |
| | DPM | ohm | | |
| | | shunt '-' |
| | | | V
| | | |
| 0V | |In- |
| o--o--o o-------------o
| | | | |
| === | | |
| GND '-----------' |
| .-.
| Load | |
| | |
| '-'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Typically, you're not supposed to connect the - of the voltage
measurement with the - of the power supply, and you're definitely not
supposed to have an input voltage greater than the power supply.

Look at the instructions again, or get in touch with the vendor. I'm
pretty sure you've got separate connections for the power supply and
the + and - inputs. If you do this right (e.g. get an isolated power
supply for the DPM, and keep it separate from the shunt resistor
input), this shouldn't be hard (as long as the DPM hasn't been smoked).

Here's one thing you can try. I'm sure your shunt resistor is OK. Use
your bench power supply to power up the DPM, with the input + and -
shorted. It should read zero, +/- one digit. Now, connect up a 1.5V
battery, a 10K resistor, and a 1K pot to the DPM like this:

| 1.5V
| |
| .-.
| | |10K
| -----------. | |
| | | '-'
| +5V | |In+ |
| o-----o o-------------o
| | | |
| | | |
| | | .-.
| | | .-->| |1K
| | DPM | | | |
| | | | '-'
| | | | |
| | | | |
| 0V | |In- | |
| o--o--o o--------o----o
| | |
| | |
| '-----------'
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

You should read from zero to about 1400 counts as the pot is turned.
If this doesn't happen, the meter is probably toast.

By the way, you might want to download Andy's ASCII Circuits so you can
better describe what you're doing, if you still need help.

Good luck
Chris

.

Relevant Pages

  • Re: Ammeter internal current draw
    ... The input impedance of your ICL7107-based digital panel meter ... The ICL7107 is very good at cancelling out 60Hz noise, ... If you've got a longer wiring length from the shunt ... yourself some protection for your DPM input. ...
    (sci.electronics.basics)
  • Re: Note to Trevor
    ... recomends them and publsihes the corrections on their website. ... It really depends on the user having test tones and an spl meter like the RS ... > measurement equipment these guys are capable ...
    (rec.audio.opinion)
  • Re: Frequency and invariance, some trivialities.
    ... (as opposed to a measurement you think is a spatial measurement only ... I think that a meter is a spatial measurement. ... I wonder what you have read about these temporal paradoxes. ... The only issue here is your confusion, ...
    (sci.physics.relativity)
  • Re: Nice CdS light detector in col_pic
    ... and use PIC internal pullup to provide the current for the LDR. ... I had an exposure meter for photography, in the times we still used film, ... good measurement, but more than adequate for photography. ...
    (sci.electronics.design)
  • Re: Measuring mA (debate solution needed)
    ... He's calculating the current in a circuit my measuring the voltage ... read the meter. ... voltage drop across the resistor is more accurate. ... Understanding measurement errors can get quite complicated, ...
    (sci.electronics.design)