™/S, MOLBLOC TERMINAL OPERATION AND MAINTENANCE MANUAL
© 1995 - 2010 Fluke Corporation, DH Instruments Division
Page 90
3.5.4.2
A+B mode
PURPOSE
To operate two molblocs simultaneously on channels A and B and
obtain a flow rate which is the sum of the flow through the two molblocs.
PRINCIPLE
In A+B mode makes measurements on one channel and then the
other channel. The flow rate displayed is the sum of the two most recent channel
readings, updated each time a channel reading is complete. This allows two
molblocs to be used together in parallel to measure flows greater than the range
of a single molbloc.
SET UP
Best results with A+B mode are obtained when the two molblocs are mounted in
parallel, symmetrically. A common regulator should be used with as little tubing,
fittings, etc., as possible between the point where flow is split upstream of the two
molblocs and rejoined downstream. Standard hardware setups (molstics) for
A+B operation are available from
DHI
.
OPERATION
To activate A+B mode, press
[SETUP]
, select
<4A_B>
and then select
<1A+B>
.
returns to the MAIN run screen in A+B mode. The MAIN run screen in
A+B mode is:
1.
Ready/Not Ready indication.
2.
Sum of channel A and channel B's two most recent
flow rate readings and the unit of flow.
3.
The gas that is being flowed.
4.
Rate of change of flow for the A+B results in units of
flow per second.
5.
Indication that A+B mode is active (if space is
available).
* 45.0775 slm N2
R 0.002/s A+B
The MFC run screens (if the has the optional MFC control feature) are
unchanged except that the top line indications are A+B flow.
3.5.4.3
A/B Mode
PURPOSE
To operate two molblocs simultaneously on channels A and B and
display the ratio of their flow rates.
PRINCIPLE
In A/B mode, makes measurements on one channel and then the
other channel. The individual flow rate measured by each channel is displayed
as it is read and information on the ratio and disagreement between the two
channels is also calculated and displayed.
This function is intended to provide a convenient, system controlled, means of
comparing two molblocs, for example to check the coherence of measurements
made by different molblocs.
SET UP
When using A/B mode to compare two molblocs, the two molblocs are connected
in series. The volume between the two should be minimized and the upstream
pressure regulation should be as stable as possible to facilitate the establishment
of the steady state flow condition that must exist for a valid comparison to be made.
When selecting the hardware setup for running an A/B mode comparison, it is
