Feedback Signal from a Control Valve

Look in here:

http://www.google.co.in/#hl=en&sclient=psy-ab&q=sipart+ps2+positioner&oq=SIPART+ps2+&gs_l=hp.1.2.0l4.0.0.1.15651.0.0.0.0.0.0.0.0..0.0.les%3B..0.0...1c.JrdRrVLQaiM&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=1d90548ed80c812d&biw=1038&bih=508

Well if you identified something about the control valve (fluid controlled, pressure range, control mechanism, manufacturer, etc.) then we might be able to guide you to an efficient way to obtain your feedback. Come to think of it, you don't even ask for an efficient method. You just asked for a possible method. I cannot draw very well but I've always admired Rube Goldberg's work.

Glue a protractor to the valve shaft and focus a web camera onto a pointer that indicates the shaft position. Send this image to a musical conductor of your local Baroque music ensemble. He will use the degree shown in the image to select the tempo and musical piece to be played by the orchestra. This music will then be piped to a musicologist with a stop watch to identify the musical composition and the beats per minute used in this performance. He'll write a review of the performance in your local paper and its web review. A grad student will copy the web review to their blog. You will read the review and translate the review to the valve position and type this value into your SCADA system.

(Just trying to add some humour.)

There are two means to read position

1) analog output 4-20mA representing position

The LY module is an analog output module option for the PS2:

2) Read the primary HART variable which is position in units of percent

The position of the valve is of less value than information about what is happening to the process variable that the valve is being used to control.