MSA MultiGard 5000 - Page 22

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3103-1001 Rev. 0
3.2.1 Flow Switch
The MultiGard 5000 System is equipped with a sample flow switch to ensure that sufficient sample
and calibration gas is applied to the sensor. The function of the bypass flow switch is to ensure that
the sample line flow rate exceeds the minimum requirements. The sample flow switch and the
bypass flow switch have been factory preset to close at the appropriate flow levels.
NOTE: If a flow switch is subjected to excessive flow rates, it may lead to a situation where the flow
switch does not respond by opening on loss of flow. Furthermore, a flow switch that is stuck closed
will prevent the unit from properly performing an internal flow diagnostic test that will result in an
incorrect “Manifold Leaks” error message. This may be corrected by tapping on the flow switch
until the desired effect is observed. If this does not correct the problem or the problem reoccurs, this
may be an indication of particle or residue accumulation in the flow switch. Under those
circumstances, the flow switch should be cleaned in accordance with the manufacturer’s data sheet
in Section 4. To clear a “Manifold Leaks” error message after a flow switch problem has been
detected and corrected, a leak test must be initiated and lead to a successful resolution. A diagnostic
leak test may be activated manually from the Diagnostics screen (see section 4.2.9).
3.3 Sample Transport Time
NOTE: Sections 3.3, 3.4 and 3.5 specifically apply to the standard MultiGard 5000 look-ahead
bypass flow scheme. Refer to Section 1 if your system employs a custom flow scheme.
To ensure that the slowest responding sensor is exposed to the gas sample for the entire analysis
time, the time it takes for the gas sample to be transported to the Multigard must be considered. To
allow for this variance in line length, a sample transport time parameter is entered when calculating
dwell time to ensure that a fresh sample is applied to the sensor(s). The sample transport time is a
function of the tubing inner diameter, length of tubing and the minimum sample line flow rate. The
standard recommended tubing is 0.250" OD, 0.175" ID nylon tubing (MSA part number 029207).
The Flow Diagram will indicate the part number for the recommended tubing for your system. Use
Table 3.1 or the equation provided below to enter the appropriate sample transport time to the
corresponding line number in the Extended Setup and Sample Transport Time screen (see section
4.2.6) .