The microampere meter
The microampere meter gives full scale deflection for 0.1 V input. The current to be measured is passed through a known resistance R and the voltage drop across it is measured.
| PARTS LIST | |
| R1 | 10KΩ |
| R2 | 10KΩ |
| R3 | 3.3KΩ |
| R4 | 100Ω |
| D1 | IN 4001 |
| D2 | IN 4001 |
| D3 | IN 4001 |
| D4 | IN 4001 |
| IC1 | LM 741 |
| M1 | 1 mA meter |
The this table shows the relationship between different values of R5 and the current that will give full scale deflection.
| R5 | Full Scale current |
| 100KΩ | 1µA |
| 10KΩ | 10µA |
| 1KΩ | 100µA |
| 100Ω | 1mA |
A high impedance Micro Ampere meter using a 741 .The operational amplifier is used as a non-inverting dc amplifier in which the negative feedback is through a dc meter requiring 1mA for full scale deflection.
Diodes D1 and D2 protect the IC from accidental excessive input voltages and diodes D3 and D4 protect the meter from overloads.
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On changing the input into a contact pad, is it possible to measure the body meridian resistance please