9Bpr - Fluke MOLBOX RFM Operation And Maintenance Manual

(ver 1.10 and higher) reference flow monitor

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Use of the HEAD function to assure in tolerance measurements is most important when

using molbloc-S at high pressures. Specifying the head height within ± 3 in. (7.5 cm) is

adequate to assure that, even in the worst case, the uncertainty on the head correction

will be insignificant relative to the tolerance of the measurement.

OPERATION

To access the HEAD function, press the [SPECIAL], <8head>. The display is:

Entry field for head height.

Current molbox RFM gas selection.

Edit the head height to the desired value. Press [ENT] to return to the run screen with the

new head correction active. Press [ESC] to return with no changes.

The reference height of the molbox RFM pressure measurement is the middle of the

molbox RFM rear panel pressure quick

connectors. The head height should be

entered as a positive value if the molbloc

is higher than the molbox RFM and

negative if it is lower.

The head function is automatically disabled when running AutoZ (see Section 3.4.4.4.2)

and in the calibration run screen (see Section 5.2.4.1)

3.6.9

<9BPR>

PURPOSE

In molbloc-S operation, to select the molbox RFM BPR (back pressure ratio) measurement

mode.

PRINCIPLE

When molbloc-S elements are used with molbox RFM, the RPT which is normally used to read

molbloc downstream pressure, may be pneumatically connected to either the molbloc-S nozzle's

upstream or downstream pressure, by molbox RFM internal valving. The two RPTs are used to

simultaneously measure upstream pressure when possible to minimize the uncertainty on

molbloc-S upstream pressure measurement by averaging the two RPT readings. The upstream

absolute pressure is the most critical measurement for calculation of the flow through molbloc-S.

Measurement of molbloc-S downstream pressure is only necessary to monitor the BPR (molbloc

back pressure ratio). The value of BPR indicates whether the flow through the molbloc-S has

achieved the necessary critical flow condition (see Section 3.1.2).

When the molbox RFM internal valves are positioned to connect one RPT upstream and the

other downstream of the nozzle to determine BPR, the valve state is referred to as BPR ON (see

Figure 11).

Edit head height:

+ 25

Page 91

3. OPERATION

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