Trane MUA-SVP01A-EN manual Reverse Acting, Direct acting

Functions

Figure 2. Direct acting

Max User SP

User Ctrl SP

80ºF 100%

override

scaler

75ºF 0%

75ºF PID 0-100%

75ºF 100%

override

scaler

>	0-100%
=	Output
<

Min User SP

70ºF 0%

REVERSE ACTING

The controller output AO-1 is modulated by a PID loop from 0% to 100% based on the User Control setpoint and the input signal to IN-9. As the input signal increases the output voltage decreases. Additionally, a secondary control acts to override the PID loop to scale the output as follows.

If the input variable equals the User Control setpoint, the output will be determined by the PID loop. In this situation the override has no effect on the output value.

If the input variable is above the User Control setpoint, the output could decrease from 100% to 0% as the input variable increases from the User Control setpoint to the Max User setpoint. In this situation the output value is the lesser of the PID output or the override output.

If the input variable is below the User Control setpoint, the output could increase from 0% to 100% as the input variable decreases from the User Control setpoint to the Min User setpoint. In this situation the output value is the greater of the PID output or the override output. See the following example.

Assume the user wishes to control the fan speed using a variable frequency drive (VFD). The VFD input is 0-10Vdc. The control variable will be building pressure. As the building pressure increases, the fan speed should decrease. The building pressure transducer has a range of -0.1" to +0.1". The user would like the building

22 Direct-Fired Indoor and Outdoor Units • MUA-SVP01A-EN