The 250 series millivolt protectors provide continuous surveillance of
high dc currents when used with current shunts, or can be used to
monitor temperatures in conjunction with thermocouples. The protector
incorporates a user adjustable trip and time delay which can be set to
initiate an alarm when the input exceeds the desired level.
Operation
When used in conjunction with current shunts the millivolt protector can be used to
monitor battery charging currents, current drain or under/over-current. Monitoring of under/
over-temperature and detection of hotspots can be achieved in applications using
thermocouples. All industry standard shunts and all popular thermocouples are supported.
The millivolt protector relays offer user adjustable trip point (set point) and time delay
settings. The time delay setting adjustment range is typically 0 to 10 seconds, although
longer delays are available. As soon as the monitored signal moves outside of the set
point limit, the time delay is activated, after which a trip will occur. The time delay
prevents the relay from tripping for a predetermined period to prevent nuisance tripping.
These products also feature an internal differential (hysteresis) setting of 1% to reduce
nuisance tripping if the measured signal is noisy or unstable. These units require an
auxiliary power supply.
Over High Trip Models
When the monitored signal exceeds the set point, the time delay is started. When the
time has elapsed, the relay will energise and the red LED will illuminate to indicate the
trip condition. The relay will automatically reset once the monitored signal falls below
the set point minus the differential. When reset, the LED will extinguish and the relay
de-energises. The time delay is not active when resetting.
Under Low Trip Models
When the monitored signal falls below the set point, the time delay is started.
When the time has elapsed, the relay will de-energise and the red LED will extinguish
to indicate the trip condition. The relay will automatically reset once the monitored
signal rises above the set point plus the differential. When reset, the LED will illuminate
and the relay energises. The time delay is not active when resetting.
Options
250 series protector relays offer various customised options to suit individual
requirements.
- Adjustment ranges – different adjustment ranges are possible for the set point and
time delay controls.
- Differential – internally fixed value between 1% and 15%.
- Relay operation – standard models are failsafe, but the relays can be customised
to energise or de-energise on trip.
- Cold junction compensation available on request.
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