Mercury Switch Type; Transducer Connection; Mop - Maximum Operating Pressure - Resource Data Management Mercury PR0018 User Manual

Mercury Switch User Guide
Operation
Once the Switch has been correctly setup, it will pass values to each of the controllers connected to ports 1 through 10. In an EEV
application the evaporator in temperature probe reading for a case controller can be obtained from the Mercury Switch on which the
controller is connected. A suction pressure transducer is connected from the case Island to the 4-20mA input of the Mercury Switch or
the pressure read from a remote plant controller. This pressure is then converted to a temperature based on the gas type being used by
the system. This temperature is transmitted to each controller connected to the switch and along with the suction temperature probe local
to the controller the superheat is calculated. Please see the Mercury Case controller user document from the RDM website for further
details. (P-51 Minimum valve opening) RDM recommend that this parameter be set to 0% when using Mercury Pressure Switch to
calculate Superheat. Please note that RDM recommend that the evaporator in temperature probe is fitted as the controller will use this to
calculate the superheat in the event of a communication loss with the Mercury Switch. (Or the remote Mercury Plant Controller) The
Mercury Case controllers require to have P17 (Evaporator control) set to 1 (Remote) for this feature to function.

Mercury Switch Type

There are 4 types: -
Type Description
1 Degree C/ Bar
2 Degree C/ PSI
3 Degree F/ Bar
4 Degree F/ PSI

Transducer Connection

Note:- Pressure/Humidity Link. The mA input is available for Pressure applications only, for Humidity please use a PR0445 connected to
the display port.
MOP – Maximum Operating Pressure
When the MOP alarm is created a valve off command is sent to the 6-5E controllers connected to the Mercury Switch. The percentage
that the valve shuts down to is dependent on the "Div Value" parameter in the Mercury case controller. When the Mercury Switch
generates the MOP alarm the controller reduces the maximum valve opening to this percentage. For example if the Div Value" parameter
is set to 50% and the MOP alarm is generated then the maximum valve opening will be limited to 50%. Therefore as the controller pulses
the valve the maximum the valve will open to is 50%.
If Mercury 6-5M controllers are connected to the Switch then the LLV will be closed when the MOP alarm is created and return to normal
operation when the alarm clears. When the pressure reduces below the MOP diff the valves will revert to normal operation at 1 minute
intervals. The number of controller coming back to normal operation per minute depends on the "recovery count" value.
Warning
Ensure that all power is
switched off before
installing or maintaining
this product
+12V loop feed mA loop return
Revision 2.1D
mA Input
Link
Selector
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Pressure
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