Laurel Electronics LTE SERIES TRANSMITTERS PULSE INPUT - Manual (Page 26)

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13. DUAL RELAY OPERATION
Dual solid state relays are standard and can operate in a basic alarm mode, in a hysteresis band
mode, or in a deviation band mode. Setpoint operation is referenced to the digital reading in
engineering units that is internal to the transmitter.
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
In basic alarm, the relay changes state automatically when the reading rises above a limit, and
changes back automatically when the reading falls below that limit. A red LED indicates that the
relay is in an alarm condition. The alarm can be programmed to be active high or active low.
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
In hysteresis band alarm, 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 hysteresis band is often used to minimize relay
chatter. A wide hysteresis band can be used for on-off control.
In deviation band alarm, the relay actuates when the reading falls within the deviation band,
and de-actuates when the reading falls outside. A deviation value (such as 50 counts) is set up
on both sides of the setpoint. Passbands are often used for component testing.