P74x/EN MT/N
1, P742, P743
(MT) 11-
1.4 Recalibration
1.4.1 P74x relay
Recalibration is not required when a PCB is replaced unless it happens to be one of the
boards in the input module, the replacement of either directly affects the calibration.
Although it is possible to carry out recalibration on site, this requires test equipment with
suitable accuracy and a special calibration program to run on a PC. It is therefore
recommended that the work is carried out by the manufacturer, or entrusted to an approved
service centre.
1.5 Changing the relay battery
Each relay has a battery to maintain status data and the correct time when the auxiliary
supply voltage fails. The data maintained includes event, fault and disturbance records and
the thermal state at the time of failure.
This battery will periodically need changing, although an alarm will be given as part of the
relay’s continuous self-monitoring in the event of a low battery condition.
If the battery-backed facilities are not required to be maintained during an interruption of the
auxiliary supply, the steps below can be followed to remove the battery, but do not replace
with a new battery.
Before carrying out any work on the equipment, the user should be familiar with the
contents of the safety section/safety guide Pxxx-SG-4LM-2 or later issue, the technical
data section and the ratings on the equipment rating label.
1.5.1 Instructions for replacing the battery.
Open the bottom access cover on the front of the relay.
Gently extract the battery from its socket. If necessary, use a small insulated screwdriver to
prize the battery free.
Ensure that the metal terminals in the battery socket are free from corrosion, grease and
dust.
The replacement battery should be removed from its packaging and placed into the battery
holder, taking care to ensure that the polarity markings on the battery agree with those
adjacent to the socket.
Note: Only use a type ½AA Lithium battery with a nominal voltage of 3.6V
and safety approvals such as UL (Underwriters Laboratory), CSA
(Canadian Standards Association) or VDE (Vereinigung Deutscher
Elektrizitätswerke).
Ensure that the battery is securely held in its socket and that the battery terminals are
making good contact with the metal terminals of the socket.
Close the bottom access cover.
1.5.2 Post modification tests
To ensure that the replacement battery will maintain the time and status data if the auxiliary
supply fails, check cell [0806: DATE and TIME, Battery Status] reads ‘Healthy’.
Additionally, if further confirmation that the replacement battery is installed correctly is
required, the commissioning test described in chapter, ‘Date and Time’, can be performed.
1.5.3 Battery disposal
The battery that has been removed should be disposed of in accordance with the disposal
procedure for Lithium batteries in the country in which the relay is installed.
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