Dwyer Instruments GFM2 Series Installation And Operating Instructions Manual Download Page 8

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The Auto Zero procedure normally takes 1 to 2 minutes during which time the DP
Zero counts and the Sensor reading changes approximately every 3 to 6 seconds.

Figure b-7: GFM2 During the Auto Zero Procedure

The nominal value for a fully balanced sensor is 120 counts. If the GFM2’s digital
signal processor was able to adjust the Sensor reading within 120 ± 10 counts,
then Auto Zero is considered successful. The status LED will return to a constant
GREEN light.

If the device was unable to adjust the Sensor reading to within 120 ± 10 counts,
then Auto Zero is considered as unsuccessful. The constant RED light will appear
on the status LED. The user will be prompted with the “AutoZero ERROR!” screen.

5.3.8 Self Diagnostic Alarm

GFM2 series Mass Flow Meters are equipped with a self-diagnostic alarm which is
available via multicolor LED, digital interface and on screen indication (for devices
with optional LCD). The following diagnostic events are supported:

5.4 Analog Output Signals Configuration

GFM2 series Mass Flow Meters are equipped with calibrated 0 to 5 VDC and 4 to
20 mA output signals. The set of the jumpers (J7A, J7B, J7C) located on the right
side  of  the  flow  meter,  inside  of  the  maintenance  window  above  the  15  pin  D-
connector  (see  Figure  C-1  “GFM2  configuration  jumpers”)  are  used  to  switch
between  0  to  5  VDC  or  4  to  20  mA  output  signals  (see Table  VI). Analog  output
signals of 0 to 5 VDC and 4 to 20 mA are attained at the appropriate pins of the 15-
pin "D" connector (see Figure b-1) on the side of the GFM2 transducer.

Table VI - Analog Output Jumper Configuration

See APPENDIX IV for actual jumpers layout on the PCB.

6. MAINTENANCE
6.1 Introduction

It is important that the Mass Flow Meter is only used with clean, filtered gases.
Liquids may not be metered. Since the RTD sensor consists, in part, of a small
capillary stainless steel tube, it is prone to occlusion due to impediments or gas
crystallization. Other flow passages are also easily obstructed.

Therefore, great care must be exercised to avoid the introduction of any potential
flow impediment. To protect the instrument, a 50 micron (GFM2-X-010) filter is built
into the inlet of the flow transducer. The filter screen and the flow paths may require
occasional cleaning as described below. There is no other recommended
maintenance required. It is good practice, however, to keep the meter away from
vibration, hot or corrosive environments and excessive RF or magnetic interference.

If periodic calibrations are required, they should be performed by qualified
personnel and calibrating instruments, as described in section 7. It is recommended
that units are returned to Dwyer for repair service and calibration.

6.2 Flow Path Cleaning

Before attempting any disassembly of the unit for cleaning, try inspecting the flow
paths by looking into the inlet and outlet ends of the meter for any debris that may
be clogging the flow through the meter. Remove debris as necessary. If the flow
path is clogged, proceed with steps below.

Do not attempt to disassemble the sensor. If blockage of the sensor tube is not
alleviated by flushing through with cleaning fluids, please return meter for servicing.

6.2.1 Restrictor Flow Element (RFE)

The Restrictor Flow Element (RFE) is a precision flow divider inside the transducer
which splits the inlet gas flow by a preset amount to the sensor and main flow paths.
The particular RFE used in a given Mass Flow Meter depends on the gas and flow
range of the instrument.

6.2.2 GFM2-X-010 Models

Unscrew the inlet compression fitting of meter. Note that the Restrictor Flow
Element (RFE) is connected to the inlet fitting. Carefully disassemble the RFE
from the inlet connection. The 50 micron filter screen will now become visible.
Push the screen out through the inlet fitting. Clean or replace each of the removed
parts as necessary. If alcohol is used for cleaning, allow time for drying.

Inspect the flow path inside the transducer for any visible signs of contaminant. If
necessary, flush the flow path through with alcohol. Thoroughly dry the flow paths
by flowing clean dry gas through.

Carefully re-install the RFE and inlet fitting avoiding any twisting and deforming to
the RFE. Be sure that no dust has collected on the O-ring seal.

AUTOZERO IS ON!

S: 405 DP: 512

The actual value of the Sensor and DP counts will vary for
each GFM2.

NOTICE

For GFM2 with RS-232 option all Auto Zero status info
available via digital communication interface.

NOTICE

Number

5
6
7

8
9
10

Diagnostic Alarm Description

Auto Zero procedure is running

FATAL ERROR (reset or maintenance
service is required for return in to the
normal operation)
CPU Temperature too high (Electronics
Overheating)
Sensor in the warm up stage (first 6
minutes after power up sequence,
normal operation, no critical diagnostic
events present)
Flow Sensor Temperature too low
Flow Sensor Temperature too high
Totalizer Reading hit preset limit

Low Flow Alarm conditions
High Flow Alarm conditions
Normal operation, no diagnostic events

LED Color
and Pattern

Not periodically
flashing RED
Constant RED

Flashing RED/UMBER

Constant UMBER

Flashing UMBER/OFF
Flashing RED/OFF
Flashing
GREEN/UMBER
Flashing GREEN/OFF
Flashing GREEN/RED
Constant GREEN

Priority
Level

4
5
6

7
8
9

[0] - Priority Level is highest (most important). When two or
more diagnostic events are present at the same time, the

event with the highest priority level will be indicated on the status LED and
displayed on the LCD (if equipped). All diagnostic events may be accessed
simultaneously via digital communication interface.

NOTICE

Analog Signal Output

Flow Rate Output

Jumper Header J7

J7.A
J7.B
J7.C

5-9

6-10
7-11

0 to 5 VDC

J7.A
J7.B
J7.C

1-5
2-6
3-7

4 to 20 mA

Digital output (communication) is simultaneously available with
analog output.