beautypg.com

Laurel Electronics LTM CTR SERIES PULSE, AC or PROCESS TOTALIZER INPUT, SERIAL DATA OUTPUT User Manual

Page 25

background image

-

- 25 -

13. DUAL RELAY OPERATION

The optional 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, rate alarm or control
would be referenced to a setpoint in RPM.

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 limit = 50
Hysteresis band = 100

Heater

OFF

R

e

a

d

in

g

ON

ON

ON

OFF

OFF

950

Setpoint = 1000
Deviation limit = 50
Deviation band = 100

Hysteresis band Deviation band


A hysteresis band
controls relay action symmetrically around a setpoint. The relay closes (or
opens) when the reading goes above the setpoint plus one hysteresis limit, and opens (or
closes) when the reading falls below the setpoint less one hysteresis limit. A narrow hysteresis