How Do I Convert PID Parameters From Gain to Time?
Primary Software: LabVIEW Toolkits>>PID Control Toolset
Primary Software Version: 6.0
Primary Software Fixed Version: N/A
Secondary Software:
Problem: I am using the PID Control Toolkit. The PID Gains input is asking for Gain, Integral Time and Derivative Time. I am familiar with Proportional Gain, Integral Gain and Derivative Gain. What is the difference between these?
Solution: The equation for a PID controller can be expressed in several ways. The three most common ways is parallel, series and ideal. Series is a simplification of ideal that makes it easier to implement in hardware. Ideal and parallel are equivalent, once the parameters have been converted. The equations are shown below in Figures 1 and 2. The only difference is that the gains have been rearranged.
- Proportional term
The proportional term is the same between the two (Kp = Kc). In the series formulation, Kp only affects the proportional gain. In the ideal equation, Kc affects integral and derivative output as well. The proportional gain may also be expressed as proportional band (PB). The relationship between the two is Kp = 100%/PB. So a proportional band of 50% is equivalent to a proportional gain of 2.
- Integral term or Reset
The integral term may be expressed as either a time or gain. Integral gain is the inverse of integral time (Ki = 1/Ti). Increasing integral time makes the output respond slower to an error, which is opposite of the effect of increasing integral gain. The integral gain in the series PID is equal to the overall gain divided by integral time in the ideal PID (Ki = Kc/Ti). For both formulations setting the integral time or integral gain to 0 will turn off the integral action.
- Derivative term or Rate
The derivative gain is in units of time. The derivative gain in the series PID is equal to the overall gain times derivative time in the parallel formulation (Kd = KcTd). Setting derivative time or derivative gain to zero turns off the derivative action.
For a complete explanation of the implementation to the PID algorithm in the PID Control Toolkit see Chapter 2 of the PID Control Toolkit User Manual.
Related Links: Manuals: PID Control Toolkit User Manual
Attachments:
Figure 1: Ideal PID equation
Figure 2: Series PID equation
Report Date: 03/05/2004
Last Updated: 03/07/2004
Document ID: 374DUJOH
