Brooks Instrument 5860i - Manual (Page 30)

Brooks ® Model 5860 i
4-6
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5860i-MFM-eng
Part Number: 541B110AAG
November, 2008
4. Install the sensor assembly (3) as shown in Figure 5-1 and secure
with the two socket head cap screws (6) and washers (7). Tighten
the screws to 28 in-lbs.
5. Install the printed circuit board (2), secure with bracket (13) and two
screws (8). Plug the connector from the sensor assembly (3) onto
the PC Board. The flow arrow on the connector should be pointing in
the direction of the flow.
6. Install the electronics cover (11) on the meter and secure with three
screws (8). Tighten the upper jack post on the D-Connector.
7. Prior to installation leak and pressure test, the assembled flowmeter
to any applicable pressure vessel codes.
4-5 Use of the Conversion Tables
If a mass flowmeter is operated on a gas other than the gas it was
calibrated with, a scale shift will occur in the relationship between the
output signal and the mass flow rate. This is due to the difference in heat
capacities between the two gases. This scale shift can be approximated by
using the ratio of the molar specific heat of the two gases, or sensor
conversion factor. A list of sensor conversion factors is given in Table 4-3.
To change to a new gas, multiply the output reading by the ratio of the gas
factor for the desired gas to the gas factor for the calibration gas.
Actual gas = Output x factor of the new gas
flow rate reading factor of the calibrated gas
Example:
The flowmeter is calibrated for Nitrogen.
The desired gas is Carbon Dioxide.
The output reading is 75 sccm when Carbon Dioxide is flowing.
Then
75 x 0.778 = 58.35 sccm
In order to calculate the conversion factor for a gas mixture, the following
formula should be used:
Where,
P1 = percentage (%) of gas 1 (by volume)
P2 = percentage (%) of gas 2 (by volume)
Pn = percentage (%) of gas n (by volume)
Example: The desired gas is 20% Helium (He) and 80% Chlorine
(Cl) by volume. The desired full scale flow rate of the mixture is 20
slpm.
Sensor conversion factor for the mixture is:
Nitrogen equivalent flow = 20/.901 = 22.20 slpm Nitrogen