™/S, MOLBLOC TERMINAL OPERATION AND MAINTENANCE MANUAL
© 1995 - 2010 Fluke Corporation, DH Instruments Division
Page 34
Several of the screen displays and functions described in this section are different
for molbloc-L and molbloc-S operation. Where the differences are major, the description of
these functions is divided into two parts.
3.1.3
Flow Ready/Not Ready Indication
The character to the left of the measured flow on the MAIN run screen provides a flow
Ready/Not Ready
indication. This indication is intended to provide the user with a clear and
objective indication of when a stable flow has been achieved.
Ready <*>
is indicated when the current stability (rate of change) of flow is less than the
stability limit. The user can set the stability limit (see Section 3.5.2). The
Ready/Not Ready
indication is often used when comparing the and a test device to help determine
when steady state flow conditions are present so that a valid comparison reading can be made.
In addition to the conditions listed in sections 3.1.3.1 and 3.1.3.2 molblocs that have named
calibration support will flash the flow display and indicate a Not Ready condition when the
measured flow exceeds the calibrated flow range by 5% or the measured upstream pressure
exceeds the calibrated pressure range by 10 kPa above the maximum pressure or 10 kPa
below the minimum pressure. The downsream pressure is used when a molbloc-L
downstream calibration is active.
3.1.3.1
molbloc-L Operation
In molbloc-L operation, the
Ready/Not Ready
indication also helps guard against
using molblocs above their valid range by monitoring the Reynolds number of the
flow. If the Reynolds number of the current flow exceeds 1 300, the
Ready (<*>
)
indicator flashes. The current Reynolds number value can be viewed using
[P&T]
(see Section 3.4.5). If molblocs are used within the pressure and flow
range limits for the flowing gas and the pressure dependent calibration type
(see Section 1.2.5), a Reynolds number of 1 200 will never be exceeded (1 300
is used as the warning limit to allow for individual molbloc differences).
Ready/Not Ready
character indications are:
<*>
Flow
Ready
(stable).
<*>
(Flashing): Reynolds number > 1 300.
<
↓
>
Flow
Not Ready
(unstable and decreasing).
<
↑
>
Flow
Not Ready
(unstable and increasing).
<P>
Flow
Not Ready, flow flashes
(pressure exceeds calibrated
pressure range by 10kPa)
<F>
Flow
Not Ready, flow flashes
(flow exceeds calibrated max flow by 5%)
3.1.3.2
molbloc-S Operation
In molbloc-S operation, the
Ready/Not Ready
indication is also used to warn the
user when the BPR (back pressure ratio) is too high to ensure critical flow (see
Section 3.1.5). When the BPR is beyond the choking limit, molbloc-S flow
measurements may not be valid and the
Ready
indicator becomes
<P>
. The
Ready/Not Ready
indicators based on flow stability are also used in molbloc-S
operation, but the
<P>
indicator takes priority over other indicators.
