Instruction manual

OM2  6
turns off Q2 by stopping it’s emitter/base current placing Q2’s collector at a
high level.
What we have is the ability to provide both a high(active high), and a low
(active low), output signal when an input is applied to the OM2. The active
high output is connected to J2 pin 2 from the collector of Q1. Active low
output is provided on J1 pin 1 from the collector of Q2.
Now that we’ve explained the operation of the output transistors the only thing
left is what capacitor C2 does. For simple DC input levels there is no need to
have C2 in the circuit. It may even be desirable to remove it if fast acting input
signals are used. But if you need to monitor an AC input signal such as an AC
power line at 50/60Hz then C2 will be required. Without it the output will
change at the rate of the input signal frequency. C2’s value is such that a
50/60Hz input signal will produce a solid output signal fro an AC input signal.
For example when the input signal is power on an AC power line the output
will be held at it’s active state until power is removed. Input signals with a
frequency from 0Hz (DC) to 250KHz can be applied and will produce a
corresponding pulsed output if C2 is not installed. With C2 installed the output
will be a stead level according to the input signal.
Diodes D1 and D2 are placed across both the active high and active low
outputs to provide protection if an inductive load such as a relay is used. This
is necessary because when a current is passed thru an inductor, the coil of a
relay for example, a magnetic field is created around it. When the current is
removed the field collapses and a voltage is induced in the coil in the reverse
direction of the original applied voltage. This voltage can be many times the
original and is the opposite polarity. This is called counter EMF (Counter
Electromotive Force) and can damage the output transistors. The diodes are
connected so they do not conduct when normal voltage is applied but conduct
when the field collapses the diodes conduct and short out the counter EMF.
They are optional and can be left in place for most applications but can be
removed if they interfere with your application.
A load that draws up to 150mA at up to 40VDC can be connected between +V
and either or both the active high and active low outputs on J2. See the
“Connecting Your OM2” section for this manual for more information about
connecting you OM2 to input and output devices.