B&B Electronics 232OPSDA manual Gain =

The signal conditioning circuit for this A/D input channel has been designed to be easily modified. In the original configuration, R5 and R6 are left OPEN (they are not present). These two spaces are provided if you need a different gain. Reducing the gain of this non- inverting amplifier allows you to measure currents up to 100mA, and increasing the gain allows you to read much smaller currents with greater accuracy. See the circuit schematic in Figure B.1 and board layout in Figure B.2 in Appendix B.

To change the gain of this non-inverting amplifier, remove R8 and R9, and calculate values for R4 and R5 using the equation below.

Gain =	V0	= 1+	R5
	10 × LoopCurrent		R4

NOTE: V0 is the voltage read by the A/D converter and (10 x loop

current) is the voltage drop across the 10Ω resistor. R4 and R5 should be chosen so that V0 does not exceed 5.00VDC.

NOTE: Decreasing the gain allows you to measure larger currents, but the maximum current that can be read is 100mA. The 100mA limit is due to the power rating of the 10Ω resistor (0.125W).

NOTE: When using the 4-20mA current loop input, A/D 1 - A/D 5 should be connected to the terminal block labeled GND.

Documentation Number 232OPSDA1397 Manual 17

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