Teledyne OT-3 operating instructions Alarm Relays, Contact ID for Failsafe Relay Operation

Installation OT-3

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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

Teledyne Analytical Instruments 16