AutomationDirect Logo DL205 Frequently Asked Questions

Product Selected: DL205
Category Selected: PID

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Question: When using the PID loops with my D2-250, my process variable doesn't look correct coming from my analog or temperature card. What's wrong?
Answer: The Setpoint Value (SP), Process Variable (PV), Bias (Integrator) and Control Output Value (CO) are in binary format. If you use the pointer method to bring the analog signals into the CPU be aware of the format you have specified. With the pointer method, if you do not precede the number of channels constant with an '8' the value is in BCD. You must do a BIN conversion before OUTing this value to Word+3 (PV). Also, make sure the proper format from the Word+5 (CO) is in the proper format when it reaches its module. It is in binary format when it leaves the PID loop. The loop table specifications are contained in the PID chapter of the User Manual.

FAQ ID: 51
Question: Why can I not get any Control Output from my PID loop?
Answer: Most likely you haven't entered a high limit for your Control Output in the PID setup. The default is 0 and the maximum is 4095 binary. Your must enter something in this field (Word+31) from the PID setup or from ladder. You should also check your Control Output word (Word+5) to see if you are actually getting Control Output. If this value is changing then make sure you are writing this value to the physical output device. This will most likely be an analog card or Time-Proportioning ladder for a discrete output point.
FAQ ID: 52
Question: Why does my Setpoint Value change in my PID loop when I go from Manual to Auto from the PID view or ladder?
Answer: You are probably in Bumpless Transfer Mode 1. In this mode, the Setpoint Value is forced to the Process Value on a manual to auto transition. You should be using Bumpless Transfer Mode 2 if you do not want this to occur. This is covered in the Bumpless Transfer section of the PID chapter in the DL205 User Manual
FAQ ID: 53
Question: How man PID loops does the D2-250-1 have?
Answer: The D2-250-1 has four PID loops. The D2-260/262 has 16.
FAQ ID: 697
Question: Where can I find documentation on the PID functions for the D2-250 CPU?
Answer: Chapter 8 of the D2-USER-M.
FAQ ID: 752