Measuring current with an LCD meter
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 10th May 2004, 01:25 PM #1 Matttcattt   diyAudio Member     Join Date: Feb 2003 Location: Bristol Measuring current with an LCD meter How can I measure current (DC) with an LCD meter? I would guess that I would mesure the voltage drop over a seres resistor, but I have no idea how to implement this. Any links, circuits or advice appreciated. __________________ If it aint broke, don't fix it. If it is broke, fix it. If you can't fix it, take it apart and see how it "worked".
 10th May 2004, 01:27 PM #2 zx3chris diyAudio Member   Join Date: Oct 2002 Location: south amboy nj To measure current you need to 'break' into a circuit. That is, you disconnect some part of the circuit and enter in your meter. Current through -- Voltage across, remember that and you will know how to measure. The number on the meter will be the amount of current flowing from your + lead to your - lead. -chris
 10th May 2004, 01:28 PM #3 peranders   Electrons are yellow and more is better! diyAudio Member     Join Date: Apr 2002 Location: Göteborg, Sweden Ohm's law That's it. U = I*R => 200 mV FSD you need a resistor with value 2 A => 0.1 ohms 200 mA => 1 ohms etc. __________________ /Per-Anders (my first name) or P-A as my friends call me Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 35 pcb's in interest.
jan.didden
diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Re: Measuring current with an LCD meter

Quote:
 Originally posted by Matttcattt How can I measure current (DC) with an LCD meter? I would guess that I would mesure the voltage drop over a seres resistor, but I have no idea how to implement this. Any links, circuits or advice appreciated.
Does this meter have a 'current' scale? If yes, you can 'break' into the circuit as described above, that is you put the meter into the line where you want to measure the current. If the meter only has 'voltage' mode, you need a shunt resistor in the line, and measure the drop across the resistor. You want to keep the resistor as small as possible to avoid changing the circuit by the measurement process.

Jan Didden
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Matttcattt
diyAudio Member

Join Date: Feb 2003
Location: Bristol
I need to re-phrase my question. By LCD meter, I meant an LCD meter module, like the one shown in the picture. They are designed to mesure voltage. How can I connect one of these to mesure current?
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 c260296-01.jpg (28.8 KB, 106 views)
__________________
If it aint broke, don't fix it. If it is broke, fix it.
If you can't fix it, take it apart and see how it "worked".

 11th May 2004, 10:28 AM #6 djQUAN   diyAudio Member   Join Date: May 2004 Location: manila you still haven't mentioned what current are you trying to measure. high voltage? AC? DC? how many amperes? how much allowable voltage drop? what is the measurement range of the LCD module?
 11th May 2004, 10:38 AM #7 Holger Barske   diyAudio Member     Join Date: Jan 2001 Location: Ruhrgebiet This seems to be a classical 3,5 digit dvm, which measures +/- 199,9 millivolts without any additional circuitry. __________________ Best regards: Holger www.holgerbarske.com
Matttcattt
diyAudio Member

Join Date: Feb 2003
Location: Bristol
Quote:
 Originally posted by djQUAN you still haven't mentioned what current are you trying to measure. high voltage? AC? DC? how many amperes? how much allowable voltage drop? what is the measurement range of the LCD module?
This is for in car use.
12v DC
>100A
Dont know...
I dont have a particular module in mind.

Quote:
 Originally posted by HBarske This seems to be a classical 3,5 digit dvm, which measures +/- 199,9 millivolts without any additional circuitry.
Yes
__________________
If it aint broke, don't fix it. If it is broke, fix it.
If you can't fix it, take it apart and see how it "worked".

 11th May 2004, 08:13 PM #9 johnnyx   diyAudio Member   Join Date: Jan 2004 Location: manchester If you find out I'd like to know. I want to monitor charging and usage of current on a boat, and 100A fsd would be about right (for now). The problem is the shunt resistor for that current. RS Components do some shunts for 200mV dmms, but not 100A ones. A Hall-Effect transducer could be used, but this is not without problems.
till
Banned

Join Date: Apr 2002
Location: Germany, Clausthal
Quote:
 A Hall-Effect transducer could be used, but this is not without problems.
http://www.allegromicro.com/sf/0752/#sample_request

Quote:
 The problem is the shunt resistor for that current. RS Components do some shunts for 200mV dmms, but not 100A ones.
i would use a piece of copper cable.

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