Hardware Installation
6 SCX 920 Installation Guide
Output Equipment Requirements
The eight outputs on the SCX 920 are universal and can be wired to pro-
vide direct digital control for virtually all electronic devices, pneumatic
analog devices, and bi-directional motors and actuators. They can be
wired so that you have Form C, analog (voltage or current), or tristate
outputs, or a combination of them.
Analog outputs can be a variable current (0 to 20 mA) or a variable volt-
age (0 to 20 V). In addition to standard ON/OFF for digital outputs and
(and ON/OFF/–ON for tristate), both digital and tristate outputs have
pulse width modulation (PWM). PWM allows you to modulate valves
and dampers to 0.1 sec resolution.
All outputs are programmable. Eight override rotary switches let you
either manually control each output or set it to AUTO so the controller
can control it.
Form C Outputs
The Form C relay of each output is rated for 5 A at 50 VAC.
Analog Outputs—Voltage
The voltage output provides 5 mA maximum output over the range of 0
to 20 VDC. The input impedance of the device being controlled can be
no less than 4000 Ω.
Analog Outputs—Current
The current output provides a 0 to 20 mA control signal. The input
impedance of the device being controlled can be no greater than 750 Ω.
The circuitry that produces the 0 to 20 mA signal acts as a “current
sourcing device.” It sources the current to ground.
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