Martel Electronics 135 - Manual (Page 41)

Safety
Good safety practices should always be followed when using high
pressures. Although liquids are considered non-compressible, dissolved
gases and trapped gases can exist in the system and can store
significant energy when compressed under high pressure. Always use
good quality fittings that are rated for the pressures being used.
Always wear safety glasses or goggles.
The ranges and resolution of the various pressure modules can be
found on page 70.
Input Functions
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The pressure adapter module receives power and commands from
the calibrator’s output section and the pressure readings are made
through the calibrator’s input section. As a result the calibrator loses
its input to output isolation any time the pressure module is plugged
into the feature connector. This is not a problem as far as pressure
measurements are concerned. However, if you are operating the
calibrator in a mode that requires input-output isolation, such as
calibrating an E to E or I to E transmitter that is loop powered from
an external 24V power supply, you MUST UNPLUG the pressure
module. To be safe, you should disconnect the module anytime you
are making simultaneous input-output electrical measurements.