General information PMD02

The master value is used to compensate for minor zero-point shifts. These lead to the detection of positive or negative leakages which, however, are not a real leak.

Even in the case of no leaky test pieces, non-zero leakage values may occur due to the physical conditions. These can be compensated with the master value:

Displayed leakage = Measured leakage minus master value

The master value will be inversely offset. The indicated leakage can thus be normalized to zero. This result leakage is then also used for the limit value Analysis.

By means of the adjustment values 1 and 2, the original measurement curve (raw values) is associated with an actual leakage. This is necessary because a "volume factor" is created by the overflow method and the overflow buffer between buffer volume and total volume. This is also noticeable at the pressure ratio of the buffer pressure to the test pressure.

The calibration is essential for correct working. For this purpose, a leakage calibrator is required as measuring means.

Procedure:

• First, determine the pressure ratio between the buffer pressure and the overflow pressure after the overflow. With this ratio, the correct buffer pressure for the desired test pressure must then be entered into the parameters.
• Then measure the first raw value (original value) for the leakage zero (calibration value 1)
• Next, set a nominal leakage with the leakage calibrator and measure the second raw value (original value) for the nominal leakage (adjustment value 2)
• Assign the nominal leakage in the parameters to the measured raw values
• Only now can the device measure correctly

The answer to this question depends on the load on the devices:

• Under heavy load (every day in multi-shift operation) the device should be checked and calibrated at least once a year
• Under less severe stress, this cycle can be extended at once in two years

Importand:

This calibration does not replace a regular check or the update / upgrade by the manufacturer. In addition, it says nothing about the condition of the device. It reproduces only a snapshot of the measuring systems of the device at a certain point in time.

To set up an on-line help, you can do the following ways:

• Copy the Windows Help file (chm) from the Docu CD to your computer. An on-line help is then available to them locally
• Copy the Web site files from the Docu CD to a server on your intranet. This data is then available to all employees at the plant

• During the filling process, thermo-dynamic processes occur in the test gas (test air), which are to be compensated at a later time by the environment. If shorter filling times are used, the test gas (test air) on the two sides of the differential pressure sensor (test volume and comparison volume) can not compensate and a curved differential pressure characteristic is produced during the resting or measuring phase. Depending on the parameters, the curve can be either upwards (direction positive values) or downwards (direction negative values). By means of a corresponding filling pressure adjustment in the filling phase 1, this effect can be counteracted somewhat.
• There are actual leaks e.g. In the testing device. In this case, however, you should first remove the leakage before setting a master value, since otherwise incorrect measurements can occur.
• There is a temperature influence. Cooling the test gas (test air) results in negative and heating to positive values. In this case as well, it is necessary to determine exactly where this temperature influence originates. In the case of constant operations, the setting of a master value can be used to counteract this effect. However, an incorrect application also leads to incorrect measurements here!

There are two methods for this:

1. Manually using a leakage calibrator
2. Automatically through the device

For a detailed description, refer to the device documentation.

The PMD02 in the variant DIFFERENTIAL PRESSURE can detect and evaluate leakage not only as pressure change per time (e.g., as Pa / s) but also as volume flow per time (e.g., ccm / min). For this conversion to be possible correctly, the PMD02 requires the value of the total test volume connected to the test side. This consists of a test piece, hose and internal device volume. This total value must be entered in the corresponding parameter of the test program.

For more information on the calculation of the volume flow from a pressure drop, please click here!

For a detailed description, refer to the device documentation.

A simple protocol is possible via the serial interface RS232 "Serial 2". The device can be set in such a way that a result telegram is sent here after each measurement. The telegrams can be recorded with a simple printer or a terminal program. In addition, it is possible to record and evaluate the data as curves and / or data records with the APT software PMD02-ANALYZE.

For a detailed description, refer to the device documentation.

A step-by-step description is available in the documentation for the device. You will find this in the following chapter:

> Create test program - Operation / remote control of the PMD02 -> Select by request -> DIFFERENTIAL PRESSURE or MASS FLOW -> build  the test program