User`s guide

one of the resistors in a circuit is proportional to the voltage across the total resistance

in the circuit.

The trick to using a voltage divider is to choose two resistors with the proper propor-

tions relative to the full scale of the digital input and the maximum signal voltage.

The phenomena of dropping the voltage proportionally is often called attenuation.

The formula for attenuation is:

For a given attenuation, pick a handy

resistor and call it R2, then use this for-

mula to calculate R1.

R1=(A-1)*R2

For example, if the signal varies

between 0 and 10 volts and you wish to

measure that with an PCI-DIO24 board

with a full scale range of 0 to 5 volts,

the

Attenuation

is 2:1 or just 2.

2 = 10K+10K

10K

The variable

Attenuation

is the propor-

tional difference between the signal

voltage max and the full scale of the

analog input.

Attenuation = R1+R2

Digital inputs can readily use voltage dividers. For example, if you wish to measure a

digital signal that is at 0 volts when off and 24 volts when on, you cannot connect that

directly to the PCI-DIO24 digital inputs. The voltage must be dropped to 5 volts max

when on. The Attenuation is 24:5 or 4.8. Use the equation above to find an appropri-

ate R1 if R2 is 1K. Remember that a TTL input is 'on' when the input voltage is

greater than 2.5 volts.

IMPORTANT NOTE

The resistors, R1 and R2, are going to dissipate all the power in the

divider circuit according to the equation Current = Voltage /

Resistance. The higher the value of the resistance (R1 + R2) the

less power dissipated by the divider circuit. Here is a simple rule:

For Attenuation of 5:1 or less, no resistor should be less than 10K.

For Attenuation of greater than 5:1, no resistor should be < 1K.

The CIO-TERMINAL is a 16" by 4" screw terminal board with two 37 pin D type

connectors and 56 screw terminals (12 - 22 AWG). Designed for table top, wall or

rack mounting, the board provides prototype, divider circuit, filter circuit and pull-up

resistor positions which you may complete with the proper value components for your

application.