Table of Contents
In general process instrument measurement, transmission, monitoring and controlling is either pneumatic version or electronic version.
Pneumatic version instrumentation
In case of pneumatic version the driving force will be instrument air.
The nominal instrument air supply will be 20 psi or 40 psi i.e., (1.4 kg/cm2 or 2.8 kg/cm2).
The output of pneumatic instrument will be 3-15 psi or 6-30 psi i.e., ( 0.2-1.0 kg/cm2 or 0.4-2.0 kg/cm2 ) at zero and span/maximum instrument range.
Electronic version of instrumentation
In case of electronic version the driving force will be electric supply.
The nominal instrument supply varies from one instrument to other. The common supplies are 115 / 230 VAC or 24 VDC.
The output from the instrument will be 4-20 mA DC or 1-5 VDC analog signal and sometimes digital signal.
Control system
Control system in any process industry may be pneumatic system or electronic system or digital control system. Depending upon the individual requirement the type of instrumentation shall be decided.
To have more reliable, safe and trouble free operations now-a-days people prefer digital control system for process control.
Transmitter
It is an Instrument which measures and then convert the concerned process measurement to a remote Indicating, Recording or Controlling device.
Transmitters are of two types – Pneumatic Type – Electronic Type.
Pneumatic Type Transmitters
In case of pneumatic version the driving force will be instrument air. The nominal instrument air supply will be 20 psi or 40 psi i.e., (1.4 kg/cm2 or 2.8 kg/cm2).
The output of pneumatic instrument will be 3-15 psi or 6-30 psi i.e., ( 0.2-1.0 kg/cm2 or 0.4-2.0 kg/cm2 ) at zero and span/maximum instrument range.
Instrument Air
Qualities of instrument air
– The Pressure of the Instruments Air shall always remain constant preferably ranging between 90 to 100 PSI ( around 7.0 kg/cm2)
– The Instrument Air should be as dry as possible
– The Instrument Air should be as clean as possible
– The Instrument Air should not contain any oil or other contaminants
Read Also