Emerson 2468CD, 2468CB manual 3c-9, 3C.3.2 ALARM AND TRIPPING FACILITIES, 3c.3.2.1 Philosophy

Hydrastep 2468CB & 2468CD Manual Opto-isolated Output Board Option

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 Mains voltages are present in this instrument when power is connected. De-energise before opening front cover.

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 3c-9