Inverse pressure control tutorial: Switching from forward to back pressure control
A forward pressure controller can be reconfigured into a back pressure controller by following two simple steps.
- First, you must swap the valve location (tutorials linked below).
- You can then activate inverse pressure control using either the front display or serial communications.
In this article, we first discuss the differences between a forward and back pressure controller and then provide instructions on making the switch.
Note: For devices with 7v firmware or earlier, this change will require serial communications.
Forward pressure control vs back pressure control
Forward pressure controller
- Upstream valve
- Downstream pressure control
- Valve opens to increase pressure
- Valve closes to decrease pressure
Back pressure controller
- Downstream valve
- Upstream pressure control
- Valve opens to decrease pressure
- Valve closes to increase pressure
Video tutorial
Step-by-step instructions (front panel)
- Switch valve position using the relevant valve swap tutorial for either rolamite valves or small valves.
- Press the bottom right button for “MENU” selection.
- Press the top middle button for “ABOUT” selection.
- Press the top middle button for “DEVICE STATE” selection.
- Press the bottom middle button for “EDIT” selection.
- Press the top left button for “EDIT REGSTR” selection.
- Use the up, down, and select digit buttons to enter the register number 20.
- Press the lower right button for “SET” selection.
- Record the current value of the register for safe keeping.
- Add 32768 to this value to activate inverse control mode.
- Use the up, down, and select digit buttons to enter this new value in register 20.
- Press the bottom right button to “SET” this new value.
- Power cycle the device.
NOTE: Registers can only be changed via the front panel on devices with 8v or newer firmware. Older devices can only edit registers over serial communication.
Step-by-step instructions (serial)
- Switch valve position using the relevant valve swap tutorial for either rolamite valves or small valves.
- If you don’t already have a serial terminal application, download Alicat’s pre-configured application here.
- Plug the device in and connect the communication cable to your PC. Open the serial terminal app.
- The terminal app will ask you for a COM port. You can find your COM port number in the computer’s device manager.
- Set the baud rate to match your Alicat (typically 19200) and hit enter. You should receive a message saying device was connected successfully. If you don’t, double check that the COM port number is correct.
- Query register 20 value by typing: AR20 and hit ENTER.
- Note: We are using a device with a unit ID of “A”. If it were “B”, the command would be BR20.
- Add 32768 to whatever value was given, and then write it by typing: AW20=[new value] and hit ENTER. (Example: My current value was 29719, so I would type: AW20=62487)
- Power cycle the device.