3.2 Alarm And Tripping Facilities; 3C.3.2.1 Philosophy; 3C.3.2.2 Opto-Output Interconnections For Alarm/Tripping Systems - Emerson Hydrastep 2468 series Operating Manual

Hydrastep 2468CB & 2468CD Manual
3C.3.2 ALARM AND TRIPPING FACILITIES
The output boards provide high and low water level alarm and trip facilities for the 2468
Hydrastep system. Four to eight opto-isolated outputs can be made available for each input
board fitted.

3c.3.2.1 Philosophy

A requirement in regulations concerning steam raising plant is the provision of an automatic
low water level shut-down or trip device. In the 2468 Hydrastep the opto-isolated output
board provides the required output signals for such devices.
In practical applications of shut-down systems two factors must be considered, the
consequences of spurious trips and the non-availability of a trip when required, due to
protection system faults.
The following opto-isolated output (for brevity this output title will be shortened to opto-
output) circuits are specific to the 2468 Hydrastep Level Indicator versions.

3c.3.2.2 Opto-Output Interconnections for Alarm/Tripping Systems

It is necessary to open the Hydrastep 2468 Electronic Enclosure to carry out any wiring,
therefore care must be taken when working inside the unit.
WARNING
Note: Before any opto-output interconnections are made it is necessary to fulfil any safety
regulations governing the plant shutdown procedures.
Since one input board receives inputs from the odd numbered electrodes and the other input
board receives inputs from the even numbered electrodes, interconnections between odd
and even opto-isolated output boards will be required. The opto-outputs are normally open
circuit and are switched into a conducting mode (short circuit) when their dedicated electrode
detects its allotted water/steam state to signal an alarm.
The following are examples of opto-output configurations used.
24685034
Mains voltages are present in this instrument when power
is connected. De-energise before opening front cover.
Opto-isolated Output Board Option
3c-9