Granville-Phillips Series 330, Instruction Manual, Page: 67 / 76

7 Process Control Module
67
Series 330 Vacuum Gauge Controller
Instruction Manual - 330004 - Rev. 02
Figure 7- 4 shows the status of the process control relay contacts for the ON and OFF conditions.
7.3.4 Manual Override
The three-position switches AT THE TOP on the front panel of the process control module (Figure
7-2) allow override of the programmed setpoints at any time. When moved to the right, the relay is
activated. When moved to the left, the relay is deactivated. When left in the center position, the
relay is controlled automatically.
7.4 Process Control Theory of Operation
The process control module contains a dedicated microcontroller and a nonvolatile memory chip
for storage of the setpoints. Since data is read/written to this chip serially, it is necessary to store
working copies of the setpoints in internal RAM memory.
The microcontroller compares the setpoints with the pressure display data on the display bus and
makes a decision as to whether or not to activate a channel's relay. The manual override switches,
when set to the ON or OFF position, take precedence over the microcontroller's decision.
7.5 Process Control Troubleshooting
The setpoints are read from nonvolatile memory into RAM when the unit powers up. On power up,
a checksum is computed and stored in RAM, and is updated whenever a setpoint is changed. It is
then periodically recomputed from the existing setpoints and checked against the preexisting value.
If for any reason (such as a power fluctuation or electrical transient in the system) a setpoint
becomes corrupted, this method will usually trap the error.
If a setpoint in the non-volatile memory is found to contain data which is not a valid setpoint, the
setpoint will be set to 0.
If the Microprocessor LED (Figure 7-3) is illuminated or flashing, there is a circuit failure.
Figure 7-4 Process Control Relay Contact Status
Relay ON
Relay OFF
Pole
Pole
NC
NO
NO
NC