Dwyer DMF User Manual

Page 19

priate relative correction factor should be recalculated see section (9).

It is standard practice to calibrate Mass Flow Meters/Controllers with dry nitrogen
gas at 70

F (21.1EC), 20 psig (1.4 bars) [25 psig (1.7 bars) for DMF 41842] inlet

pressure and 0 psig (0 bar) outlet pressure. It is best to calibrate the DMF trans-
ducers to actual operating conditions. Specific gas calibrations of non-toxic and
non-corrosive gases are available at specific conditions. Please contact your dis-
tributor or Dwyer for a price quotation.

It is recommended that a flow calibrator of at least four times better collective accu-
racy than that of the Mass Flow Controller to be calibrated be used. Equipment
required for calibration includes a flow calibration standard and a certified high
sensitivity multimeter (which together have a collective accuracy of +0.25% or bet-
ter), an insulated (plastic) screwdriver, a flow regulator (example: metering needle
valve) installed upstream from the Mass Flow Controller and a pressure regulated
source of dry filtered nitrogen gas (or other suitable reference gas).

The gas and ambient temperature, as well as inlet and outlet pressure conditions
should be set up in accordance with actual operating conditions.

7.2

Calibration of DMF Mass Flow Controllers

All adjustments to the DMF calibration and control loop tuning are accomplished
using the RS485 (or optional RS232) interface in conjunction with setup and cal-
ibration software available from Dwyer. The sensor zero is automatically adjust-
ed internally whenever the control valve is fully closed (set point less than 2% of
full scale) and the unit is warmed up.

DMF Mass Flow Meters may be field recalibrated/checked using the setup and
calibration program for the same range they were originally factory calibrated for.
Flow range changes may require a different Restrictor Flow Element (RFE).
Additionally, a different Solenoid Valve Orifice for the DMF Mass Flow Controller
(see Table VI) may also be required. Consult your distributor or Dwyer for more
information.

TABLE VI DMF SOLENOID VALVE ORIFICE SELECTION TABLE

ORIFICE PART NUMBER

FLOW RATE [N

]

OR.010

Under 10 sccm

OR.020

10 to 1000 sccm

OR.040

1 to 5 slpm

OR.055

5 to 10 slpm

OR.063

10 to 15 slpm

OR.073

15 to 20 slpm

OR.094

20 to 50 slpm

OR.125

50 to 100 slpm