Temperature compensation sample code for PLC blending application

Is there any sample PLC code or code for sale that allows temperature
compensation through RTD 4-20mA analog inputs and uses table API 6b?
The application is a four-loop PID blender that mixes four ingredients
that change in volume depending on temperature. The temperature
compensation would multiply the gross recipe volume by a factor in the
table to give the net volume required at that temperature. Allen
Bradley RSLogix 500 for MicroLogix 1500 code is preferred, but any
similar ladder logic will be acceptable.

Sounds simple, but I think you will have to find someone to write this bit of code for you. Regards Alan Case

Why do you require temperature compensation calculations? If you use 3 wire RTDs and the correct linearised transducer, the transducer does it for you. Same with thermocouples. I always use the right transducers and have never had to calculate compensation yet. Sounds like you have the wrong gear. By the way, if you require accuracy, never use 2 wire RTDs. Also be very carefull that the 3 wires coming back from the RTD are of the same material and cross sectional area or you will get inaccurate figures.

Apparently, I didn't explain my problem well enough. I am not compensating for errors in the RTD input, but rather for the volume of material passing through the blender. The following is from literature about a similar blend controller:

Automatic Temperature Compensation
The e-BLEND Controller includes automatic temperature compensation as a standard feature to allow blending on a net volume basis. With this feature the e-BLEND will accept temperature inputs from each blend component loop and automatically convert the measured gross volume to an equivalent net volume at a reference temperature, 600F or 150C. This computation is based on the latest API tables or by linear slope. Computation formulas for the API Standard 2540, Tables 6A, 6B and 6D and temperature slope algorithm are included in the standard e-BLEND software and selectable by a simple data entry item.

My controller is only concerned with the 6B and temperature slope algorithm.


Another source describes the problem as this:

All such volumes will be corrected to standard conditions (60°F and equilibrium vapor pressure) by the application of correction factors listed in “Petroleum Measurement Tables” API Standard 2540, latest revision (Table 6A for JP-4; Table 6B for all other Petroleum
Products).

One more source describes the table as:

Table 6B - Generalized Products, Correction of Volume to 60 Degrees F Against API Gravity at 60 Degrees F

The table is quite lengthy and I believe there is a formula that may not be exact but that is used in electronic controllers for obtaining the values in the table. This formula is what I really need. I can probably figure the ladder logic out myself.

I'm sure you have this done by now, but I just joined and thought I'd let you know. I have done code that will do what you want. It's done using GE Fanuc logic, but I'm sure you could convert it would any problems. PM me if you are still needing help.