Laurel Electronics LTA DPM SERIES ANALOG INPUT - Manual (Page 23)

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15. DUAL RELAY OPERATION
The dual solid state relays can operate in a basic alarm mode, in a hysteresis band mode, or in a
deviation band modes, as explained below. Setpoint operation is referenced to the digital reading
in engineering units that is internal to the transmitter. For example, temperature alarm or control
would be referenced to a setpoint in °C or °F.
Time
1000
D
ig
it
a
l
R
e
a
d
in
g
Setpoint
OFF OFF
ON
Time
1000
Setpoint
OFF
ON ON
D
ig
it
a
l
R
e
a
d
in
g
Active High Basic Alarm Active Low Basic Alarm
A basic alarm changes state automatically when the reading rises above a specified limit, and
changes back automatically when the reading falls below that limit. A red LED indicates the
relay is in an alarm condition, which can be active high or active low, as programmed.
Time
R
e
a
d
in
g
1050
950
Pass
Fail
Fail
Time
1050
Setpoint = 1000
Hysteresis value = 50
Heater
OFF
R
e
a
d
in
g
ON ON ON
OFF OFF
950
Setpoint = 1000
Deviation value = 50
1000 1000
Pass
Hysteresis Band Alarm Deviation Band Alarm
A hysteresis band alarm controls relay action symmetrically around a setpoint. The relay
closes (or opens) when the reading goes above the setpoint plus one hysteresis value, and
opens (or closes) when the reading falls below the setpoint less one hysteresis value. A narrow