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Chapter 5 Trouble-shooting and
repair
Repair procedures may only be performed by
authorized personnel!
5.1
Changing PhD Ultra sensors
The PhD Ultra is designed to recognize the “Smart
Sensors” that are currently installed. Once a sensor
is recognized, the instrument automatically sets
itself up with the appropriate alarm settings for the
sensor. The instrument automatically notices when
changes have been made to the sensors installed
since the instrument was last turned on.
Note: Any changes made to the sensors
installed, even changing one sensor for another
of the exact same type will trigger a “Needs Cal”
message the next time the instrument is turned
on. The PhD Ultra must be recalibrated before
being returned to service following any sensor
change.
The PhD Ultra must be turned off prior to removing
or replacing sensors. A Phillips screwdriver is used
to remove the three screws securing the sensor
cover to the PhD Ultra case.
To replace a sensor:
(1) Make sure the PhD Ultra is turned off.
(2) Remove the three philips screws from the
sensor cover and remove the sensor cover.
For replacement of existing sensors perform
steps A3 and A4.
(A3)
From the outer surface of the sensor cover
gently push out, with a flat blade screwdriver,
the metal screen, gasket/spacer, filter/snap ring
assembly in the position above the sensor(s) to
be replaced and discard it. The metal screen is
not to be reused and its absence will not affect
performance.
(A4)
Remove any remaining traces of adhesive
from the recessed hole in the sensor cover.
Then proceed to step C5 or D5 depending on
the sensor type.
For first time sensor installation perform steps
B3 and B4.
(B3)
From the outer surface of the sensor cover,
push out yellow dust cap with a blunt tool.
(B4)
Remove sensor blank from the sensor
compartment. Then proceed to step C5 or D5
depending on the sensor type.
For Sensors O
2
, LEL, CO, CO Plus, H
2
S, NO
perform step C5
(C5)
Place the new filter/snap ring assembly, with
ridge side up, onto the recessed hole in the
sensor cover. Firmly press into place. Then
peel the backing paper from the new rubber
gasket and place, adhesive side down, centered
over the newly mounted filter/snap ring
assembly. Now proceed to step 6.
For Reactive Gas Sensors: SO
2
, NO
2
, PH
3
, HCN,
Cl
2
, ClO
2
perform step D5.
(D5)
Place the new teflon spacer onto the
recessed hole in the sensor cover. Firmly press
into place. For optimal sensor response, there
is no sensor cover-mounted, external filter
element used with these sensors. Now proceed
to step 6.
(6) Press the replacement sensor into place.
(7) Replace the sensor cap.
(8) The new sensor must be allowed to stabilize
prior to use. The following chart gives a
breakdown by sensor type with the required
stability period for current PhD Ultra sensors.
The instrument does not need to be turned on
while new sensors are stabilizing, but
functioning batteries must be installed in the
instrument. If the instrument is a NiCad unit, it
may be placed in a powered charger for the
duration of the stabilization period.
Sensor Stabilization
Period
Oxygen (54-04-90)
1 hour
LEL (54-04-80)
5 minutes
All PhD Ultra toxic
sensors except those
shown below
15 minutes
54-04-04 NH
3
Sensor
54-04-06 NO Sensor
24 hours
9. The PhD Ultra will automatically recognize the
changes that have been made upon turn on and
display the “Warning Needs Cal” message.
10. Recalibrate the PhD Ultra with calibration gas
appropriate for the new sensor before the
instrument is put back into service.
PhD Ultra programming includes safeguards to
recognize maladjusted sensors. If the settings on
the new sensor are significantly different from those
of the old it will trigger a message that the sensor is
