Differential Amp Schematic Please

[Victor Demjanenko June 15, 2018 at 1:18 pm Post count: 0]

#29871 Reply |

Hi I have a
<h1 id=”title” class=”a-size-large a-spacing-none”><span id=”productTitle” class=”a-size-large”>DROK Digital Multimeter DC 6.5-100V 100A</span></h1>
https://smile.amazon.com/dp/B017BDQHE6/ref=twister_B01MR96QPJ?_encoding=UTF8&psc=1

I understand how to connect this meter to the low side of a battery.  I have a long wire (about 20ft) from the current shunt to the meter.  The current draw of the meter (15 to 20ma) produces a slight voltage drop across this cable (resistance about 0.5ohm).  This offsets the current measurement I am trying to achieve accurately.  I know the problem is in the first first stage differential amplifier.  I have used LT Spice to simulate my condition and I have a very simple fix to eliminate this error.  I need to change the resistor on the + OpAmp terminal connection to be the negative sense lead instead of the battery return lead.  My simulations give a near perfect result after this even with LONG wires.

So may I please have a piece of your schematic that show the refdes for the differential opamp used at the front stage of the current shunt measurement.  I need to figure out which resistor to change and where to connect it.

I do NOT need your standard wiring diagram showing me how to connect the four leads of the meter to the circuit being measured.

Thanks.

 

 

[DrokKeymaster June 20, 2018 at 10:00 am Post count: 2971]

#29885 Reply |

Hello Victor Demjanenko，

Thanks for writing in.

But we are sorry technicians doesn’t allow to show schematic, we can’t get it from them. Hope you can understand.

Best regards.

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