g.Alarm Relay Characteristics
The ALARM 1 and ALARM 2. Outputs of the Alarm Relay Assembly are provided by two identical single-pole double-throw relays. Relay contacts are rated:
| | | |
5 amperes | 240 | VAC resistive |
1 ampere | 240 | VAC inductive |
5 amperes | 120 | VAC resistive |
3 amperes | 120 | VAC inductive |
5 amperes | 30 | VDC resistive |
3 amperes | 30 | VDC inductive |
Removal of AC power from the analyzer, as in a power failure, de-energizes both relays, placing them in alarm condition.
Switching characteristics of the ALARM 1 and ALARM 2 relays are as follows:
ALARM 1 Relay - The ALARM 1 relay coil is de-energized when the meter needle moves downscale through the value that corresponds to setpoint minus deadband. This relay coil is energized when the needle moves upscale through the value that corresponds to setpoint plus deadband. See Figure 2-5A, page 2- 6.
ALARM 2 Relay - The ALARM 2 relay coil is de-energized when the meter needle moves upscale through the value that corresponds to the setpoint plus deadband. This relay coil is energized
when needle moves downscale through the value that corresponds to setpoint minus deadband. See Figure 2-5B, page 2-6.
Alarm Reset - Normally both the ALARM 1 and ALARM 2 functions incorporate automatic reset. When the meter reading goes beyond the pre-selected limits, the corresponding relay is de-energized. When the meter reading returns within the acceptable range, the relay is automatically substituting an external pushbutton or other momentary-contact switch for the jumper that normally connects the RESET terminals on the Alarm Relay Assembly. If the corresponding relay is now de-energized, i.e., in alarm condition, the relay remains de-energized until the operator momentarily closes the switch.
Fail-Safe Applications - By appropriate connection to the double-throw relay contacts, it is possible to obtain either a contact closure or a contact opening for an energized relay. Also, either a contact closure or a contact opening may be obtained for a de-energized relay.
It is important that, for fail-safe applications, the user understand wheat circuit conditions are desired in the event of power failure and the resultant relay de-energization. Relay contacts should then be connected accordingly. Refer to Figure 2-6, page 2-6.
