Calculating The Sampling Frequency - Trane Tracer MP501 Installation, Operation And Maintenance Manual

of the situation, which can destabilize the system. The control system should always wait to
process the result of a change before making another change.
Figure 17
acceptable. If the sampling frequency is too fast (2 seconds), the process variable begins to oscillate
and finally destabilizes because the PID loop output drives the actuator to extremes.
Figure 17. System stability with different sampling times

Calculating the Sampling Frequency

Table 8
good initial values, but it may take some trial and error to find the best frequency.
Table 8.
Application
Duct static pressure
Discharge-air temperature
Space temperature (typical comfort zone)
Space temperature (high air change zone)
Duct humidity
Space humidity
It is possible to manually calculate the starting point for the application sampling frequency.
To calculate the sampling frequency:
19. Manually control the analog output to 0%. For example, control a heating valve closed.
CNT-SVX08F-EN
shows the process variable if sampling times are too fast, acceptable, and barely
Sampling freq. = 10 s
shows suggested program execution frequencies for common applications. These are
Suggested starting sampling frequencies
Sampling freq. = 20 s
Sampling freq. = 2 s
(system destabilizes if
sampling freq. is too fast)
Time
Suggested Execution Frequency
5 seconds
10 seconds
60 seconds
30 seconds
10 seconds
30–60 seconds
PID Control
35