PP Systems EGM-4 User Manual

Maintenance
EGM-4 Operator's Manual – Version 4.19
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Checking EGM-4 Raw A/D Readings
On the EGM-4, monitor the raw A/D readings on the display. To do so from the main menu
(1REC 2SET 3CAL, etc.):
1. Press Key 0 (to go into system diagnostics)
2. Press Key 1 (Diagnostics)
The display will show the current A/D readings for the CO
2
analyzer for both “Measure” and
“Zero” mode. Press key Z to check the analyzer zero. At this point, CO
2
free air will be
passing through the analyzer. When completed, the raw A/D reading for the analyzer zero
will be displayed in the upper right hand corner (i.e. Z:51235).
The raw A/D reading with CO
2
-free air must be greater than 40,000 and less than 52,000.
Once the raw A/D reading with CO
2
-free air is in the range 40,000 to 52,000, the instrument
should perform normally and accurately. If you are unable to achieve raw A/D readings in the
range of 40,000 to 52,000 after replacement of the infrared source, the SOT resistor (R38)
should be changed. The SOT resistor is located on standoffs near the detector end of the
sample cell making it easy to identify on the PCB and for easy soldering. The resistor can be
any value between 0 ohm and 1000 ohms that makes the zero reading between 40,000 and
52,000. Lower SOT resistor values increases the gain and increases the zero A/D reading. If
you are unable to achieve raw A/D readings in the range of 40,000 to 52,000 after
replacement of the infrared source, contact PP Systems for advice (see PP Systems’ Contact
Informationon page 7).
At this point, it would be prudent to perform a single point calibration with a reference gas if
possible (See 3CAL on page 35).
EPROM
The firmware and factory measured calibration factors for the EGM-4 are stored on a memory
chip commonly referred to as an EPROM inside the instrument. This should never require
maintenance but it may need to be replaced if the system is upgraded.
The EPROM that is used in the EGM-4 must be protected from static electricity. As a result,
there are several precautions that the customer should take before removing EPROMS. The
risk of damage can be minimized by earthing both the operator and the lab bench surface.
This can be done by covering the surface of the bench with a conductive material (e.g.
aluminium foil) that is electrically connected to an earthing point such as a metal water pipe or
tap. The operator should also be earthed using a wrist strap or by holding a wire that is
connected to the same earthed point. Please contact PP Systems for further information.
Once suitable earthing arrangements have been made, the EGM-4 enclosure can be opened
to gain access to the circuit board containing the EPROM. The position of the EPROM is
shown above.
Each EPROM is located in a specific orientation. Before starting to remove the chip, note the
position of the notch on the end of the chip relative to the rest of the instrument. Using a
small, flat screwdriver, gently pry the EPROM up until it is removed from its socket. When
fitting the new EPROM to the socket, be careful not to bend any pins. Place the EPROM in
the socket (noting the notch on one end of the EPROM) and gently press down to secure in
place.
Very Important. After replacing the EPROM, you should reinitialize the instrument (See
Initialisation on page 43).

PP Systems EGM-4 Specifications

General

Brand	PP Systems
Model	EGM-4
Category	Monitor
Language	English