If a transmitter operate with an electrical supply, then it is called electronic transmitter. The input supply for an electronic transmitter is 24 v dc and standard output of an electronic transmitter is 4- 20 mA dc of rated span of instrument.
The sensing part is basically electrical sensors of process variable. For example, for measuring level or flow capacitance differential pressure capsule are used and for temperature in RTD platinum is used. The transmitting part is generally an electronic circuit which generates 4- 20 mA with respect to the sensing input.
Electronic transmitters are classified into two types. They are,
1. Analog transmitter (NON-SMART)
2. Digital transmitter (SMART)
Analog Transmitter :
Early Analog Transmitter were widely used before arrival of SMART transmitter but still this type of transmitter are exist. Analog Transmitter also provide 4-20 mA output. On electronic circuit of transmitter it contain zero and span screw. It doesn't contain microprocessor so you can't connect it with HART.
For calibration of such type of transmitter you can adjust zero and span.
Below is block diagram of analog transmitter
SMART Transmitter :
Single module addressable ranging transmitter contain inbuilt microprocessor which open easy communication option. All SMART transmitter can talk to HART. It also gives us 4-20 mA output.
Calibration become easy as we can easily check different point using HART or using any calibrator we can check loop too.
Below is block diagram of SMART Transmitter.