Operating Instructions

Chapter 1—Introduction
Principles of Field Panel Operation
18
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Siemens Industry, Inc.
Owner's Manual
553-104
Building Technologies
2018-10-01
Executing Control Programs
The PXC Compact continuously executes a user-defined set of instructions called the
control program. This program uses the most recent point values and the most recent
clock time. The control program does the following:
● Evaluates control strategies.
● Uses an internal calendar and time clock for time-based functions.
● Updates point values and commands field points according to the program results.
● Sends messages or reports to proper terminal locations as needed.
Example
During occupied hours (7:00 A.M. through 5:00 P.M.) a fan:
● Turns ON if the room temperature rises above 80°F (27°C).
● Turns OFF when the temperature drops below 73°F (23°C).
Between 5:00 P.M. and 7:00 A.M. the fan turns OFF regardless of the room
temperature.
If the temperature rises to 85°F (29°C) at any time, the PXC Compact sends an alarm
message to an alarm printer.
These specifications can be met by:
1. Connecting a room temperature sensor/transmitter and fan starter output to the
PXC Compact.
2. Defining the room temperature sensor with a high alarm limit of 85°F (29°C) and
the fan points in the PXC Compact database.
3. Writing a short control program that defines your control strategy.
4. Enabling the execution for that portion of the control program.
To perform this control strategy, the PXC Compact:
● Continuously executes the control program.
● Samples a current or voltage signal representing the room temperature and
updates the value associated with that temperature in its memory.
– If the temperature rises to 85°F (29°C), then the PXC Compact sends an alarm
message to the printer.