What is the difference between smart positioner and normal positioner. Please add some additional info regarding IO count for both the positioners. Do they possess both AI and AO or just AI ?

 

Smart positioners are simply based on latest digital electronics, onboard CPU etc. They are capable of communicating through digital network such as HART, Fieldbus, Profibus etc. They are able to provide many critical diagnostic data locally and also through the digital communication network. Normal positioner e.g. traditional electronic positioners are based on analog electronics and they can't provide many critical diagnostic data or can't be connected to a digital network. Both of them could be connected over AO signal from the DCS. Smart positioner could be connected over analog or digital network and could provide many useful advanced features. For example you can connect a smart positioner over a 4-20 mA loop, but can collect the real time valve position feedback over the same loop using HART protocol. You don't have to buy another valve position feedback transmitter for this.

 

A normal positioner is an electropneumatic device that controls the position of a valve actuator based on a 4–20 mA analog signal from the controller.
It compares the input signal (representing the desired position) to the actual valve position and adjusts the actuator pressure accordingly.
A smart positioner is a microprocessor-based device that also receives a 4–20 mA signal.