ACR Electronics SmartReader Plus Reference Manual page 64

SmartReader Plus Data Loggers
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marked "10k" must be 10,000 ohms ±1% or better.
The value of the resistor (R) and final Range can be calculated with the following equations:
25mA Channel
The 25 milliamp channel can be modified to span higher ranges (greater than 25mA DC) by
adding a single resistor across the input terminals as shown in Figure 7-5. The value of the
resistor (R) can be calculated by the following the formula below, based on the desired current
input range (Iin) in mA**:
** Where: 500 = max input voltage in mV
25 = max current input in mA
Make sure the resistor can withstand at least twice the power you will be sending it. To
calculate this, use the following equation:
Where:
P = Minimum Power Rating of resistor (in watts)
Iini= Maximum amperage expected through resistor (in Amps)
R = Resistor value (in ohms)
For example, a 20 ohm resistor calculated to measure currents up to 50mA will require a
Figure 7-4: Modified 200mV Channel
R = 40,000 x Ein - 10,000
Ein = (R + 10,000) / 40,000
R = 500 / (Iin - 25)
2
P = 2 ´ I ´
i n
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