Looking to calibrate a -1.8 to 5.0 “H2O transmitter. Not sure what pressures to use for the 4-20 output? New to instrumentation, first one of these I’ve come across.

 

I assume that 'calibrate' means configuration of the 4-20mA range for what 4mA represents and what 20mA represents.

But I can't answer that question because there's no application 'context'.

A transmitter was purchased for a given task. Is the measurement into the vacuum gauge pressure required for the process? If so, then the negative gauge pressure range needs to be part of the range output by the transmitter.

Is the full 5.0"w.c. range a suitable maximum value for the process?

The 4-20mA range is configured (on a 'smart transmitter) to match the process conditions. Maybe a subset of the available range is needed, maybe not.

You need to ask whomever is using/designed/implementing the process for what the output range of the transmitter should be.

 

Looking to calibrate a -1.8 to 5.0 “H2O transmitter. Not sure what pressures to use for the 4-20 output? New to instrumentation, first one of these I’ve come across.

Use a pressure source 5 inch water equal 1244.2 Pascals or 0.18 psi to calibrate at 20 mA
Use vacuum -1.8 inch water equals 448 Pascals or 0.065 psi to calibrate at 4 mA

 

Use a pressure source 5 inch water equal 1244.2 Pascals or 0.18 psi to calibrate at 20 mA
Use vacuum -1.8 inch water equals -448 Pascals or -0.065 psi to calibrate at 4 mA

 

Sam gave you the Conversions. David gave you the Questions for the person who bought the device for you. Was your real question what was needed to Calibrate it.??? A Precision Pressure simulator. A Druk, Ametek, Moore Pressure Regulator in inches of water...or Similiar..
If it's a Differential pressure Transmitter you can put the pressure in the low side hookup for the Vaccumn testing part. High side is the Common for the Positive pressure part.. It can be Reversed also..Most Techs now just enter the Values with a Smart Programmer or order it Calibrated Set up upon purchase..
You Tube is also your Friend..Hope you got your Question answered..