Specifications

3. OPERATION

When the TARE function is activated, molbox RFM’s internal valves operate to

pneumatically connect together the two absolute transducers, and both legs of

the microrange option differential transducer if present, at the molbloc operating

pressure. The user can select whether this pressure is the upstream or

downstream molbloc pressure so that the tare can be made at the pressure that

will be held stable during operation (generally by a regulator or because it is

open to atmosphere). Activating the tare causes molbox RFM to record the

current differential as the tare value. The tare value will be used to correct all

subsequent RPT readings. For the absolute transducers the tare value is the

difference between the two transducer readings (hi - lo). The upstream RPT will

be corrected by (- tare value/2) and the downstream RPT will be corrected by (+

tare value/2). For the microrange differential RPT, the tare value is the differential

value read. The differential transducer will be corrected by subtracting the tare

value from the current reading.

1. High Isolation: Open

2. Low Isolation: Closed

3. Bypass: Open

4. Mirorange Bypass: Open

Figure 5. molbox RFM

Internal Pneumatic Schematic – TARING, UPSTREAM molbloc-L OPERATION

 OPERATION

At a minimum, the TARE function should be executed whenever the operating

pressure of the molbloc is changed significantly, at the beginning of each

test or any time a significant zero error is observed. For best results, it is

possible to tare before every reading since taring can be executed while

flowing. Best results will be obtained if the TARE function is executed with a

stable flow through the molbloc.

To access the TARE function press [TARE], <1tare>.

The display is:

Select tare pressure:

1upstream 2dnstream

Selecting <1upstream> will tare the molbox RFM RPTs at the molbloc’s

upstream pressure (see Figure 5). Selecting <2dnstream> will tare the RPTs at

the molbloc’s downstream pressure (Low isolation valve open, High isolation

valve closed). Select the position where the pressure will remain the most stable

during molbloc operation.