9
Chapter 1 PhD Ultra Description
1.1
PhD Ultra capabilities
The PhD Ultra gas detector can be configured to
meet a wide variety of requirements. This chapter
provides an overview of many of the features of the
PhD Ultra. More detailed descriptions of the
features of the PhD Ultra are contained in the
subsequent chapters of this manual.
1.2
Methods of sampling
The PhD Ultra may be used in either diffusion or
sample-draw mode. In either mode, the gas sample
must reach the sensors for the instrument to register
a gas reading. The sensors are located inside of the
instrument under the sensor grill cover.
In diffusion mode, the atmosphere being measured
reaches the sensors by diffusing through vents in
the sensor compartment cover. Normal air
movements are enough to carry the sample to the
sensors. The sensors react quickly to changes in
the concentrations of the gases being measured.
Diffusion-style operation monitors only the
atmosphere that immediately surrounds the
detector.
The PhD Ultra can also be used to sample remote
locations with either the hand-aspirated sample-
draw kit that is included with every PhD Ultra, or
with a motorized continuous sample draw pump that
is available separately. During remote sampling,
the gas sample is drawn into the sensor
compartment through the probe assembly and a
length of tubing.
Use of the sample draw kits is covered in
Chapter 2.
1.3 Multi-sensor
capability
The PhD Ultra can be configured to simultaneously
monitor oxygen, combustible gases and vapors and
up to two toxic gases. Sensors can be added,
removed and replaced in the field. The PhD Ultra
microprocessor and “Smart Sensor” circuitry
eliminates the need for manual switch setting and
other laborious set-up procedures.
It is necessary to verify the accuracy of the PhD
Ultra by calibration with known concentration
test gas whenever a change is made to the
sensors installed in the instrument.
The PhD Ultra design uses highly specific,
electrochemical toxic sensors that have been
designed to minimize the effects of common
interfering gases. These sensors provide accurate,
dependable readings for toxic gases commonly
encountered during confined space entry and other
industrial applications. A wide variety of toxic
sensors is available for use in the PhD Ultra.
In addition to sensors designed to measure specific
toxic hazards, Biosystems also offers a dual
purpose electrochemical sensor designed to detect
both carbon monoxide and hydrogen sulfide. The
“CO Plus” sensor is ideal for situations requiring use
of a single sensor to monitor for both toxic hazards.
Different measurement units are used depending on
the gas being measured:
Sensor Range
Resolution
LEL
0 – 100% LEL
1% LEL
O
2
0 – 30 %/Vol.
0.1%
CO
0 – 1000 PPM
1 PPM
H
2
S
0 – 200 PPM
1 PPM
SO
2
0 – 150 PPM
0.1 PPM
NH
3
(-04 version)
0 – 50 PPM
1 PPM
CO Plus
CO: 0 – 1000 PPM
H
2
S: 0 – 200 PPM
1
PPM
Cl
2
0 – 50 PPM
0.1 PPM
ClO
2
0 – 15 PPM
0.1 PPM
NO
0 – 350 PPM
1 PPM
NO
2
0 – 50 PPM
0.1 PPM
HCN
0 – 100 PPM
0.2 PPM
PH
3
0 – 20 PPM
0.1 PPM
NH
3
(-21 version)
0 – 100 PPM
1 PPM
Table 1.3. PhD Ultra Ranges and Resolutions by
Sensor Type
Sensor configuration procedures are discussed
in greater detail in section 2.5.
1.4 Calibration
The PhD Ultra detector has been designed for easy
calibration.
Accuracy of the PhD Ultra
should be checked periodically with known
concentration calibration gas. Failure to check
accuracy can lead to inaccurate and potentially
dangerous readings.
Accuracy may be verified at any time while the
instrument is in normal operation. Press the mode
button three times within two seconds to place the
instrument in “Auto-Calibration Mode”.
Calibration is a two step procedure. In the first step
the PhD Ultra is taken to an area where the
atmosphere is fresh and a "zero" adjustment is
made automatically by pressing the on / off mode
button.
The second step is the sensor response or "span"
calibration adjustment. In this step the accuracy of
the sensors is verified by exposing them to known
concentration calibration gas. Once again, if
necessary, the sensitivity or “span” is adjusted
automatically.
Calibration procedures are discussed in detail in
Chapter 3.
