4�3 Sample And Exhaust Tubing Calculations - Honeywell Midas User Manual

4.3 Sample and Exhaust Tubing Calculations
The following tables show the flow rate, tubing
length, transport time, and maximum pressure and
vacuum at the inlet and exhaust points. Tubing
lengths vary among gases. See
recommended lengths.
Table 4-1. Inlet sample specifications
Inlet Sample Specifications:
Tubing Length, m (ft)
Transport Time (sec), ID 1/8"
1
Transport Time (sec), ID 3/16"
Sample Point Vacuum
(Negative pressure)
Flow rate, cc/min.
Tubing OD, mm (in)
Tubing ID, mm (in)
1 Honeywell Analytics recommends thick-wall tubing (1/8" ID)
for best speed of response. Due to its lower surface area, thick-
wall tubing may require less conditioning than thin-wall tubing.
2 The flow rate is electronically maintained at approximately
500 cc/min and may vary within acceptable tolerances.
Table 4-2. Outlet sample specifications
Outlet Sample Specifications:
Tubing Length, m (ft)
Back Pressure at Exhaust Point
(Excluding tubing)
Tubing OD, mm (in)
Tubing ID, mm (in)
Appendix B
Maximum
30 (100) 20 (66) 10 (33)
28 19 10
63 43 23
-25.4 cm H O (-10 in H O) Maximum
2 2
500 (Flow is constant)
2
6.35 (0.25)
3.18 (0.125)
Maximum
30 (100)
20.3 cm H O (8 in H O) Maximum
2 2
6.35 (0.25)
4.76 (0.188)
Midas
Note
Honeywell Analytics recommends the use of
Teflon FEP (Fluorinated Ethylene Polymer)
tubing to assure proper sample transport.
The properties of Teflon FEP make it the
for
best choice for transporting sample toxic
gases to instruments when compared with the
properties of other similar tubing materials.
If the pressure/vacuum on the inlet/exhaust lines
does not meet the recommended values in Tables
4-1 and 4-2, the following chart describes potential
fault conditions that may be brought on by the
0
external influences thus resulting in an F81 Flow
1
Fault.
1
External Flow
Low
1
(0-150 cc/min)
Low
2
(0-150 cc/min)
min flow swings)
Medium
3 (~200-450 cc/
min)
High
4
(> 600 cc/min)
4-7
Gas Detector
®
Fluctuation Fault 81
None No Midas
®
Midas
®
gradually. If external flow
Yes changes are large and rapid,
(up to 100 cc/ Likely the final reading will be
different from what Midas
expected. Midas
Fault 81.
Minimum flow rate for the
pump is ~300 cc/min. With
this external flow, the auto-
adjust cannot work because
Yes and No Yes
the pump cannot produce
a flow at this low level. The
problem is worse if there are
flow fluctuations.
Midas
®
external flow. Midas
Yes and No Yes
issue Fault 81 due to high
flow
Explanation
will auto-adjust
changes the flow
®
® will issue
cannot reduce the
will
®