Trane PID Control User Manual

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PID loops are carried out by programs, such as process control language 
(PCL) programs and Tracer graphical programming (TGP) programs. 
Since the PID calculation occurs when the program executes, the sam-
pling frequency and the program execution frequency are generally the 
same. 

Table 2 shows recommended program execution frequencies for common 
applications. These are good initial values, but it may take some trial and 
error to find the best frequency.

You can also manually calculate the sampling frequency.

1.

Manually control the analog output to 0%.

For example, control a heating valve closed.

2.

Record the measured variable when it stabilizes.

The temperature stabilizes at 70°F (21°C).

3.

Manually control the analog output to 50% or 100%.

Control the output to 100% (completely opening the heating valve).

4.

Record the measured variable when it stabilizes.

The temperature stabilizes at 120°F (49°C)

5.

Subtract the measured variable determined in step 2 from the mea-
sured variable determined in step 4. This is the change in the mea-
sured variable.

120 – 70 = 50°F (49 – 21 = 28°C).

Note:
Tracer controllers have different approaches to using the sam-
pling frequency. For Tracer MP580/581 controllers, the sam-
pling frequency can be a multiple of the program frequency. The 
Tracer AH540 controller has a pre-determined sampling fre-
quency. The Tracer MP501 controller has a setting for the sam-
pling frequency.

Table 2: Recommended initial sampling frequencies

Duct static pressure

5 seconds

Building static pressure

120 seconds

Discharge-air temperature

10 seconds

Space temperature (typical comfort zone)

60 seconds

Space temperature (high air change zone)

30 seconds

Duct humidity

10 seconds

Space humidity

30–60 seconds