Application Note...

PCS400 Pressure Calibration System

Application:

Utilizing special gases in a pressure controller

Challenge:

An instrument manufacturer wanted to supply a gas other than air at a precise pressure to a gas chromatograph. In order to use a precision pressure controller rather than a mechanical regulator, a technique was needed to purge the controller to guarantee that only the desired gas was applied to the chromatograph.



Solution:

Mensor provided a PCS400 and a procedure to purge the controller prior to use. The procedure included a pneumatic schematic of external equipment and the instructions. The purpose was to displace the air in the controller and insure that no air was introduced during operation.

The additional equipment included a one liter volume, four valves, two vacuum pumps, and one check valve. The volume was used to move enough media through the system to display any air in the unit. The check valve was used to insure that air could not enter through the exhaust port while switching between modes.

 

The purge procedure consisted of three steps;

Step 1 - Preliminary Pressure Purge

1. Turn the pcs400 ON, and place it in the STANDBY mode.

2. Apply the special gas supply at the required pressure up to the full scale range of the PCS400.

3. Set the external valves as follows: #1 open, #2 normal, #3 diverted, #4 normal.

4. Select the CONTROL mode on the PCS400.

5. Set the control point to full scale pressure and wait until stable.

6. Command less than 1/10 of full scale pressure and allow it to stabilize.

7. Repeat steps 5 and 6 above.

8. Proceed to Vacuum Purge.

Step 2 - Vacuum Purge (after completing the preliminary gas purge described above.
    1. Turn the vacuum pumps on.
    2. Close external valve #1
    3. On the PCS400, select the MANUAL SOLENOID mode from the TEST menu.
    4. Activate valves L1, L2, L3, L5, (and L6 if so equipped). The display in the MANUAL VALVES mode should show "111011" for the valve actuation. The functional location of these valves in the PCS400 is shown in the pneumatic schematic on page 1.
    5. Reset the external valves #2, #3 and #4 to diverted.
    6. Pump for 10 - 15 minutes. Note: This time will vary widely depending on the capacity of the vacuum pumps and degree of purging desired.
    7. Reset external valves #2 and #4 to normal.
    8. The vacuum pumps may now be turned off.
    9. Proceed to Final Gas Purge.

Step 3 - Final Gas

    1. Open external valve #1.
    2. Repeat steps 4 through 6 of the Preliminary Gas Purge above.
    3. Command a low control pressure compatible with the device under test (DUT).
    4. The system has now been purged and filled with the special gas. The PCS400 can be used in MEASURE, CONTROL, OR STANDBY modes with the special gas. To continue, make sure the DUT is connected and then reset external valve #3 to Normal.
 
CAUTION: To avoid re-introducing atmospheric air into the system, DO NOT use the VENT mode on the PCS400 after starting the purge process.

Related Equipment:

The following equipment was used or recommended for this design:

  • Swagelok 40 Series Valves or Whitey Ball Valves, 2 and 3 port versions
  • Vacuum Pumps: Sargent Welch Series 1300
  • Circle Seal Check Valves
  • Hoke Cylinders

In most applications, equipment from other manufacturers could have been used. The application and the design approach used will dictate the actual items selected.