Measurement Computing CIO-DAS16/M1 - Manual (Page 34)

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The most convenient way to use solid state relays is to purchase a Solid State Relay Rack. A SSR Rack is
a circuit board with input amplifiers to switch the SSR. It has sockets to plug in modular SSRs. SSR
Racks are available from Computer Boards and most manufacturers of SSRs.
If you only want to drive one or two SSRs, use a 74LS244 output buffer chip between the 82C55 output
and the SSR. The SSR will need a 5V power source as well.
6.6 VOLTAGE DIVIDERS
If you wish to measure a signal which varies over a range greater than the input range of a digital input,
use a voltage divider. If properly designed, it will drop the voltage of the input signal to a safe level the
digital input can measure.
Consider Ohm's law, which states, Voltage = Current x Resistance
and Kirkoff's voltage law which states, the sum of the voltage drops around a circuit is equal to the
voltage drop for the entire circuit.
Thus, any variation in the voltage drop for the circuit as a whole will have a proportional variation in all
the voltage drops in the circuit.