Measurement Problem :
Today's pressing need in many industries is the measurement
of the Oxygen, specially with fuel scarcity and its high cost.
Conventional Oxygen Analysers suffer from major Limitations; a
costly, unreliable & high maintenance sampling system, dry
analysis rather than total or wet, long time delay, and inaccurate
measurements in stack.
In a zirconium oxide sensor when two sides are exposed to different
oxygen concentrations, it develops a voltage across the two sides.
This phenomenon is described by the Nernst equation which states
that the voltage generated is a function of absolute temp., Gas
constant, Faraday's constant and the logarithm of the ratio of
partial pressure of oxygen on the two sides of the sensor.
E = 0.0496 T log 10 --------------
Sensor Output, mV
T = Absolute sensor temp. Deg K ( Deg C + 273)
P1 02 = Reference air partial pressure (20.9%)
P2 02 = Sample gas partial pressure
atmospheric air (20.9% O2) is used as reference. The output becomes
the inverse logarithm of partial pressure of Oxygen and in direct
proportion to temp., of the measured gases. In hot measured gases
with temps, above 600°C, a non heated probe is used. In gases
with lower temps. a heated probe is used where sensor 2 temp.
is held constant with proportional temp. controller. In this case
the output voltage becomes proportional to the inverse logarithm
of partial pressure of oxygen of the measured gas. As the Oxygen
concentration decreases, the voltage increases giving increased
sensitivity in low oxygen concentrations.
Many of the Oxygen Analysers even today use sampling systems though
gas sample is not to be cooled and conditioned. RASKIN leads the
way having patented construction oxygen probes using space age
materials and robust common sense.The zirconia sensor is located
in the tip of the IN-SITU probe, which is wetted by the flowing
gases, unlike other designs where the gas sample is aspirated
to the sensor located outside or at the other end of the tip.
Thus RASKIN systems do not need pumps, sample probes, cooling
/ conditioning, in short no sample maintenance / conditioning.
Probes are available in lengths 200-1100 mm (longer probes on
A rugged sheet steel enclosure houses an extremely versatile electronics
Where necessary, (in case of heated probe) a separate probe heater
control box is provided.
The highly stable, high input impedance amplifiers have been designed
to operate over wide measurement ranges. As a standard, probe
temperature and O2 mV are also digitally indicated, in addition
to volume % (or PPM) oxygen. The oxygen content is continuously
calculated and displayed, by programming the Nernst equation,
based on actual sensor temperature & O2 mV values. This enhances
the accuracy. The electronics is microprocessor
based, where O2 mV, temperature and % (or PPM) oxygen are digitally
indicated, with linear, isolated, 4 - 20 mA output, Hi & Lo
O2 alarms, probe outside operating temperature range alarm, etc.
are provided. Systems
equipped with high temperature unheated probes, presence of CO
alarm (Hi O2 mV) is provided as a standard.
Using the patented probe and with long varied experience in the
field of furnace technology, various systems are built for different
In conventional analysers, heated low temperature probe is located
in the stack, where flue gas temperatures are much below ignition
(< 600°C). Here oxygen is measured not only as left over
(excess air) after combustion is complete, but air that has leaked
in between combustion chamber and stack. Errors due to reconstitution
of gases during cooling also creep in. In case of sampling systems,
analysis also is affected due to leaks in sample line, accumulated
dust, etc. RASKIN, using a high temperature, unheated probe, have
overcome the above limitations. The unheated high temperature probe
is positioned downstream of the combustion chamber where combustion
is complete, but the temperatures are still above ignition (600°C).
This provides true wet analysis - what you really wanted to know
- precise Air : Fuel ratio. This enables providing explosive mixture
present (presence of Hi CO) alarm.
- True wet measurement, eliminates
- Only requires mains electricity
- Used with any fuel, high
accuracy fast response
- Solid state, no moving parts
- Logarithmic sensitivity
increases with decreasing oxygen concentration
- Available with 200-1100mm
insertion length Probes
- Special Explosion-proof
± 10% 50Hz.
(longer probes on request)
||Prob : Upto
100°C Electronics - Upto 45°C
|ST : 600-1100°C
|HT : 900-1500°C
of reading or ±0.1% O2, whichever is greater.
(or separate instrument grade air required)
|Warm up time
(ST / HT)
upto 500 m optional
Equipment such as Cement Kilns / some types of Boilers, have highly
dusty atmospheres. High temperature unheated probe is located "IN-SITU"
in the combustion gas stream. Since no sampling / aspiration techniques
are used, dry dust settling on filter still allows gas to diffuse
to the sensor. In addition less dust settles on filters due to high
velocity of gases. Therefore, frequency of cleaning is far less.
Further, special "IN-SITU" dust cleaning arrangements,
by purge air are provided.
In most of the gas generators (except endo / exo gas generators),
the gas in which oxygen analysis is to be carried out, is at ambient
temperatures, a heated zirconia oxygen probe is used. The sensor
is maintained at higher temperature with provision of temperature
controller, heater power source with tapped transformer. The usual
instrument cabinet, with the addition of temperature controller,
is provided. Any desired oxygen measurement range is provided to
suit the generators.