Teledyne OT-3 - Manual (Page 24)

Installation OT-3
Teledyne Analytical Instruments 16
• 4–20 mA % Range: Current increases with increasing oxygen
concentration, from 4 mA at 0 percent oxygen to 20 mA at
full scale percent oxygen. (Full scale = 100% of programmed
range.)
• SSR POWER (AC units only): Provides 15vdc at 698 ohm
impedance to power external Solid State Relays.
3.3.3 Alarm Relays
The three alarm-circuit connectors are screw terminals for making
connections to internal alarm relay contacts. There is one set of contacts
for each type of alarm. Contacts are Form C, with normally open and
normally closed contact connections capable of switching up to 0.2
ampere at 125 VAC into a resistive load (0.9A for 30 VDC).
The alarm relay circuits are designed for failsafe operation. In
failsafe operation, the relays are energized during normal operation. If
power fails the relays de-energize (alarms activated).
The contact connections are indicated diagrammatically on the rear
panel as Normally Closed, Common, and Normally Open. Figure 3-2
explains how these act in failsafe operation.
Alarm 1 and Alarm 2 can both be configured as either HI or LO. A
HI alarm will activate when concentration is above threshold, while a
LO alarm will activate when concentration is below threshhold.
Figure 3-2: Contact ID for FAILSAFE Relay Operation