Integer input range of analog module

Hi,

     I have to clear one doubt ,

    In 13 bit resolution,  fallowing are the word structure

     In this case, we cannot measure value 1,2,3,4,5,............

     Only we can read the values like 4,8,12,16,20,............

     This may effect on accuracy.

This Means 723.4 nA. * 4 =  2893.6 nA.

                                                = 0.0028936 mA.

     Also, this means we can measure the current in the step of 0.0028936 mA. below this or changes in current below 0.0028936 mA. was not measurable.

The 15% over range is provided to prevent your digital value from going negative, when connected to most instruments.

Many instruments will report analog values over 20mA if the sensed value exceeds the calibrated range of the instrument. This is useful to many people who analyze the process, and troubleshoot instruments and systems. Emerson Process Systems usually top out at 20.8mA to 21.2mA when the process input is over-range, the output level goes over 20mA to indicate saturation.

Some alarm conditions can be detected by the transmitter sending between 21.75 and 22.5mA to the control system (NAMUR Levels). The Siemens scaling allows the PLC to read those values as a positive value without going negative, and not clamping the value so you are not flying blind.

On old systems, when 20mA was set to 32767, if the design of the instrument circuit had just a small error, and your PLC card measured 32768 or higher, many PLCs interpret this value as a signed value, so your instrument value suddenly goes negative, which will upset the process if you are not prepared for this.

So this has nothing to do with the Siemens side, it is all to accommodate everyone else who makes 4-20mA instruments.

This is a great thread, I just wanted to know what values to use in my programming which appears to be simply a 0-27648 integer. = 4-20mA signal

it looks like it comes from a 16 bit digitisation I.e. 2^16 / 2 (for positive and negative values = 32768 (2  Xy 16 on your scientific calc) but most of the negative range is ignored and a portion of the upper range is too.

The reasoning for this I do not understand as it seems to be a waste of resolution, my guess is this is a factor of safety used by the PLC to identify faulty components?

Hope this helps Thanks

Volkan

Please have a look the excel file for all info in one place only hexadecimal part is missing can be added later :)

 Dear Sir, 

               If possible please add hexadecimal values for better understanding.