Laversab 6600 User Manual page 68

Rev. b4 high accuracy automated pressure controller

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Refer to section 3.2.3 on how to change units. During the warm-up period, purge the system

with Dry Air by cycling the pressure at the Pt port between 60 inHg absolute and 1 inHg

absolute (or lower), at least three times.

During the warm-up period, ensure that the leaks in the system are within acceptable limits.

At 1 inHg absolute, the leak rate must not exceed 0.030 inHg/min. At 60 inHg absolute, the

leak rate must not exceed 0.030 inHg/min. To determine the leak rate, control the Pressure

Standard to the desired pressure, hold the pressure for 5 minutes to allow any temperature

effects to subside, then isolate the control mechanism from the Pressure Standard and

measure the leak rate. If the Pressure Standard is a Dead Weight Tester, the leak rate should

be low enough to ensure that the maximum allowable sink rate of the Dead Weight Tester is

not exceeded.

Towards the end of the warm-up period, perform a repeatability check at 60 inHg. Take the

pressure down to about 5 inHg and then back up to 60.000 inHg. Wait for 2 minutes, then

note the Actual value on Pt as "R1". Again, take the pressure down to about 5 inHg and then

back up to 60.000 inHg. Wait for 2 minutes, then note the Actual value on Pt as "R2". The

difference between "R1" and "R2" must not exceed +/- 0.002 inHg.

Step 3. After the warm-up period is over, using the Pressure Standard, generate a pressure of

1.000 inHg absolute. Allow the pressure to be stable at 1.000 inHg for 2 minutes and note the

actual values for Pt on the 6600. This is the "As Found" reading for the Pt Vacuum Test Point

(please see Fig. 6.1 below). It will indicate the zero drift since the previous calibration.

Step 4. Generate a pressure of 60.000 inHg absolute, allow the pressure to stabilize for 2

minutes and note the actual value for Pt on the 6600. This is the "As Found" reading for the

Pt Full Scale Test Point (please see Fig. 6.1 below). It will indicate the zero plus slope drift

since the previous calibration. Leave the pressure at 60.000 inHg while you perform the next

step.

If you do not wish to make a calibration adjustment, but just want to verify the accuracy of the

6600, please skip to Step 10.

Step 5. To make a calibration adjustment for the Pt output, on the 6600, move to the the

CALIBRATION screen using the NEXT SCREEN key and enter the password. The calibration

screen appears as follows:

Vacuum:

F.S.

CALIBRATION

Pt inHg

1. ________

3. ________

2. ________

4. ________

Ps inHg

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