Home What is Flue Gas Analysis? Testo Solutions Definitions & FAQ’s Calibration & Service Downloads Contact Us  
Definitions & FAQ's
  Definitions & FAQ's
Analyser Box
The Analyser Box (testo 350) is a rugged plastic housing that contains the: sensors, pumps, gas conditioning system (Peltier chillier and pump), valves, electronics, etc, The Analyser Box also contains a complete operating system that enables it to be used as a stand alone device that can be programmed to log measurements (250, 000 readings) for automatic semi continuous operation. The Analyser Box can also be operated remotely (to 3000 ') with a data bus cable, or in a more traditional sense, with the "control unit docked" as a suitcase Analyser.
Condensate Trap
A clear acrylic container located on the side of the Analyser Box that serves as a reservoir for condensate. The condensate water can be removed by 1) opening the plug, 2) attaching a hose to the drain port, or 3) by removing the condensate trap. Remove the trap by pulling the trap away from the Analyser and drain by shaking the trap.
Control Unit
The hand-held Control Unit "S" is the interface used to operate the Analyser Box. The Control Unit houses: system software, a user-defined back lit display, a thermal paper printer and connection ports. Complete Analyser control is through the handheld.
Dilution System
A system that expands the range of the CO sensor by introducing a specific volume of "dilution air" through a precision valve assembly. The dilution system exclusively operates with the CO sensor. Dilution factors (1, 2, 5, 10, 20 or 40) are selected by the user by pushing a function button. The values are automatically calculated based upon the factor. The benefits of the dilution system include :
  • Testing high-concentration CO sources without over-ranging and damaging the CO sensor.
  • Protecting and extending sensor life.
  • Eliminating the need for multiple sensor with multiple ranges therefore minimizing the cost-of-ownership.
An additional "Overall Dilution System" is also available at the touch of a button. It extends the range of all sensors (except O2 and CH) by a factor of 5x.
Excess Air (ExA)
A calculated value that determines the amount of "extra" oxygen in a typical burner / boiler application. The Analyser will display a percentage of oxygen above the "perfect" (or stoichiometric) condition for complete combustion. In general, excess air dilutes and cools the combustion process, it absorbs the energy (heat), and reduces the efficiency of the combustion process.
Flow and Mass Flow
The testo 350 measuring system can determine flow, velocity, and mass flow by a variety of methods. A vane anemometer and hot bulb probe can be connected to the control unit for non-combustion flow measurements. However, typically in combustion sources, the differential pressure sensor and a pitot tube is the standard method. The Pitot tube can be exposed to the harsh environment in a stack. Input variable such as: pitot factor, stack diameter, absolute pressure, humidity and the Analyser will automatically calculate mass flow in lb/hr, ton/year, etc.
Fresh Air Purge / Valve
The purge valve (standard part on testo 350 XL) mechanically opens the fresh-air gas path to remove flue gases from the Analyser. This fresh-air purge is required for electrochemical sensors in order to have accurate response and long sensor life. This valve provides a means to perform long-term testing by maintaining electrolytic equilibrium within the sensor. Fresh air purges nearly eliminate sensor drift and saturation due to long term testing or high concentration loading The valve offers a side benefit that allows the flue gas probe to remain in the stack during Analyser start up or during automatic tests. By pushing the function button, the fresh air valve immediately pulls in air from the side of the Analyser. The days of climbing the stack and fumbling with the probe are gone.
Function Keys
Four round blue buttons located directly below the display of the Control Unit. Each user-defined function key provides a shortcut to important Analyser functions. Some example include: Start sample "Pump", or "Print" emission results, or transfer the measurement values into the memory "mem", etc.
Non-Heated Sample Line (testo Patented) (NO2/SO2-Hose)
testo's non-heated sample line provides the sampling performance that is equivalent to a reference-level heated sample line. By incorporating: high velocity sample transport through a patented PTFE inner hose, minimized surface area, reduced residence time, and unique self-cleaning abilities, this technology eliminates the cost and bulk of heated sample lines.
O2 Reference
A concentration value that is reported in relation to a know reference. Regulatory authorities, engineering studies or other standard reporting may required a gas species (i.e. NOx or CO) to be reported to a specific O2 reference. This provides a method of comparing emission rates on an equivalent basis. For reporting, it eliminates the variability of having extra or deficient oxygen in a combustion system.
Over-Range Protection
The testo 350 has automatic sensor over-range protection. Whenever this limit is reached a fresh air rinse pump starts and purges the sensors with fresh air. The user can easily define the threshold for each sensor.
Pellister (CxHy Sensor)
A heated sensor that measures total hydrocarbons. Also know as a catalytic or heated bead sensor. It consists of specially matched pair of precision resistive thermal devices (RTDs) overlaid with two different coatings. The first one is covered with a propriety catalyst that creates an exothermic reaction to the presence of targeted hydrocarbons. The second RTD is covered with an inert coating and acts as a reference. Both RTDs are heated to approximately 950°F to increase the catalytic reaction rate. In the presence of hydrocarbons the catalytic RTD will have higher heat value than the reference. The RTDs are tried to two legs of a "Wheatstone Bridge" to maximize the output and stability.
testo's unique cross calibration techniques essentially make the HC module blind to interference gases such as carbon monoxide and free hydrogen.
Peltier Cooler
The testo 350 is equipped with "Peltier" principle sample gas cooler (named after the French inventor Peltier). An electric current flows through the interface surface of two different metals thereby cooling one side and heating the other. The hot wet sample gas is exposed to the cold side element. This cooling process condenses the moisture thereby drying the sample. The testo 350 controls the current on the Peltier cooler to continually remove moisture from the stack gas. The condensed water is removed with a peristaltic pump and transported to the condensate trap.
Pitot Tube
A Pitot tube is a device that uses a two tubes that are configured to measure pressure thereby permitting the calculation for flow velocity. The testo 350 utilizes pressure sensors that measure the dynamic and static pressure through the Pitot tube configuration. By entering either manual or measured input parameters (i.e. temperature, humidity, pitot factor, etc.) flow velocity is automatically calculated. With the testo straight and standard "L" shaped Pitot tubes, nearly any application can be measured.
Power / Battery / AC Operation
The testo 350 Analyser Box operates with AC line power (90-260VAC/50-60Hz) or through the "memory free" metal nickel hydride battery pack for up to 2.5 to 3 hours. Additional battery packs can be swapped out and connected as needed. (note: the batteries do not charge during AC operation)
Sensor Upgrade Model
An upgrade module is a measuring sensor that contains the original release information in order for the Analyser to measure a specific parameter. Once a module is installed in an Analyser it cannot be used again to upgrade additional Analysers, however, it can be used as a replacement or spare sensor.
testo Databus
A databus system is integrated into every testo 350 Analyser. It permits two-way communication (data transfer and function) through multiple devices (i.e. multiple Analyser boxes connected to analog output boxes connected to logger boxes, etc.). The maximum distances from end to finish is 3,000 feet. The testo-Databus can be used in 2 ways :
  • One Control Unit, as the master control, in a serial system where each device can be operated simultaneously but displayed individually by scrolling through the display on the control unit display.
  • Via CAN Bus or PCMCIA-Card as a parallel system where you can see and operate up to 16 Analyser Boxes at one time (e.g. for simultaneous reading of NOx on one computer screen).
  • The CAN Bus/PCMCIA-Card (Personal Computer Memory Card International Association) enables the Analyser Box to be operated without the Control Unit. With this configuration, multiple Analysers can be connected in a bus system (maximum of 16 Analyser boxes) and specific parameters can be assigned and displayed on a single screen as a graph or table, etc. It is a unique system and especially useful for: SCR balancing, Catalyst efficiency testing and research, and remote monitoring.
Trigger Input / Switch
The testo 350 Analyser Box has a socket that accepts a command (electrical signal) that will start a pre-configured automatic program. An external device can "trigger" the Analyser to start and stop sampling and monitoring (i.e. flip of a relay after exceeding a set limit).
This is understood to mean the penetration of gases or gas mixtures into liquids or solid substances. NO2, for instance, is absorbed/fixed by rubber or silicone hoses.
Adsorption takes place if gases are held solely by the surface forces when they come into contact with a solid substance, e.g. the inside wall of a hose. These "captured gases are then given off again uncrolledly (e.g. the presence of No2 ls indicated even though no more NO2 gas is applied).
Calibration Adjustment or Span
To adjust the measured reading to the smallest possible deviation according to the known standard value or reference (i.e. for Analyser calibration gas). Therefore, adjustment requires a change of the instrument settings.
Calibration Check
Comparison of an Analyser's output signal (measured reading) to a known standard.
The characteristic of sensors to react not only to the target gas to be verified, but also to other gases.
Error of Measurement (accuracy)
Indicated measurement minus the true value of the measured variable. This can be represented in a variety of ways :
  • Relative deviation from the measured value
  • Deviation relative to the limit value of the measuring range
  • Absolute indication, for instance as vol.% or ppm.
Deviation from the correct values of the measured values displayed across a measuring range.
Measuring Range
This is the concentration range in which the target gas can be measured by the sensor/unit with the specified accuracy.
The combination of elements with oxygen. In gases, for instance, the oxidation of NO produces NO2.
Reproducibility (Repeat Accuracy)
Standard deviation of a series of measured values from measurements performed at short intervals of time and carried out according to a defined measurement procedure by the same operator on the same parts, using the same equipment and at the same place.
Response Time
Period of time the sensor/unit needs in order to react to the introduced concentration with a stable signal/indication. In practice, txy times are given, e.g. T90 time. This is the length of time until 90% of the introduced concentration is displayed.
Slope / Sensitivity
Sensor signal per admitted (unit of) concentration. This is determined in adjustment and is stored for later measurements.
Zero Point
What the sensor signal unit displays in the absence of the gas to be verified (="target gas").
Questions on Sensors
Electrochemical Sensors
  Electrochemical sensors are devices that measure flue gas constituents (O2, CO, NO, NO2, SO2, H2S) through the principle of ion selective potentiometry The sensor contain a electrolytic matrix that is designed for a specific gas to be detected. Two or three electrodes (again gas specific) are placed in this matrix and an electrical field is applied. Flue gas enters the sensor and chemically reacts (oxidation or reduction) on the electrode releasing electrically charged particles (ions). This reaction causes the potential of this electrode to rise or fall with respect to the counter electrode. With a resistor connected across the electrodes, a current is generated which is proportional to the concentration of gas present. The output is converted then displayed as a concentration (typically in ppm, percent, or as a mass unit (i.e. lbs/hr or mmbtu).

Standard electrochemical sensors are affected by various environmental factors including: temperature, pressure, and other combustion gases. However, testo sensors are designed to eliminate these effects. Mounted on each sensor is a circuit board that contains calibration data, linearity data, and other critical information. This technology enables the sensor to be pre-calibrated at testo and installed in the field as a simple plug-in device. No need to have calibration gases on site. Additional technological advancements in sensor and Analyser design include the use of :
  • Continuous temperature compensation to provide accurate response regardless of ambient temperature fluctuations.
  • Control of sample pressure and automatic flow rate monitoring to eliminate pressure related effects.
  • Sensor temperature control by using heated thermoplastic sensor blankets.
  • Integrated on-board interference filter media that eliminates the hassle of replacing NOx beads
  • Automatic cross compensation for interference gases.
Are the sensors temperature compensated?
  Yes. Most electrochemical Analysers use temperature compensation to eliminate drift due to temperature change. Analysers typically base their compensation on the temperature when the Analyser is first turned on. The sensor output will remain linear within a limited temperature range depending upon the Analyser and sensor configuration. The testo 350 utilizes continuous temperature compensation and sensor temperature control to ensure accuracy. Sensor temperature measurement integrated circuit boards on each sensor provide the mechanism to apply a continuous temperature compensation based on sensor temperature monitoring. Still further, the thermoplastic blankets that cover each sensor provide a thermally stable environment for linear output throughout the operating range, even down to 20° F.
Can you use a NO standard range and NO low range sensor simultaneously?
  Not at the same time. Instead, you can switch or swap them in the field. This is easily done without tools and usually takes less than a minute. This innovative feature is made possible by the integrated circuit board and plug & play connectors mounted on every 350 sensor. The circuit board memory contains critical calibration, linearity, and performance information that enables the sensors to be pre-calibrated before shipping. This eliminates the downtime and shipping cost of returning the Analyser to the factory.
What is the error message "NO measurement not possible for 2 hr."?
  This is a result of the Nitric oxide sensor losing its "bias" charge. All electrochemical NO sensors require a tiny amount of electrical current in order for the sensor to measure accurately. When an Analyser is off, this current is supplied by a trickle charge from the battery. If the battery goes completely dead, then the NO sensor will loose its bias charge. The testo 350 needs approximately 2 hours to re-establish its bias charge.
How are sensors protected?
  The Analyser will automatically turn-off the sampling pump at a predefined over-range concentration. In addition, by simply pressing a function button, a fresh air purge or CO shut off or sensor zero can be started. Lastly, when the Analyser is turned off it will go through a shut-down sequence that purges residual gases from the Analyser resulting in longer sensor life and more stable output.
What is a CO dilution system?
  The dilution system extends the measurement range of the CO sensor and protect it from high eoncentrations (x40). The system has user-selectable factors (2, 5, 10, 20, 40); an automic feature and an overall Analyser function.The Analyser automatically calculates and displays the corrected concentration based upon the dilution factor. Basically, the dilution system introduces a precise volume of ambient air into a mixing chamber that contains the flue gases thereby reducing the concentration by a specific quantifiable factor. This system has many advantages over older technologies in that: it protects and extends the life of the sensor by reducing the concentration and it eliminates the cost for additional replacement sensors. The CO dilution system is standard in the Engine Kit #3 and Turbine Kit #4.
What is the reason for fresh air purges?
  Periodic fresh air purges rejuvenate electrochemical sensors. Without a fresh air purge electrochemical sensors will become "saturated' and the output will drift. The amount of time for the purge is generally dependent upon the flue gas concentration and the time of exposure. The higher the concentration and longer the exposure, the more often the fresh air purge is needed. The fresh air purge function can be started manually or automatically in the program mode. A chart for the recommended purge cycles is in the appendix in the 350 M/XL manual.
How does the Hydrocarbons (CxHy) sensor work?
  Electrochemical sensors are devices that measure flue gas constituents (O2, CO, NO, NO2, SO2, H2S) through the principle of ion selective potentiometry The sensor contain a electrolytic matrix that is designed for a specific gas to be detected. Two or three electrodes (again gas specific) are placed in this matrix and an electrical field is applied. Flue gas enters the sensor and chemically reacts (oxidation or reduction) on the electrode releasing electrically charged particles (ions). This reaction causes the potential of this electrode to rise or fall with respect to the counter electrode. With a resistor connected across the electrodes, a current is generated which is proportional to the concentration of gas present. The output is converted then displayed as a concentration.
  Standard electrochemical sensors are affected by various environmental factors including: temperature, pressure, and other combustion gases. However, testo sensors are designed to eliminate these effects. Mounted on each sensor is a circuit board that contains calibration data, linearity data, and other critical information. This technology enables the sensor to be pre-calibrated at testo and installed in the field as a simple plug-in device. No need to have calibration gases on site.
Questions on Testing
What is NOx?
NOx is a term used to describe nitrogen oxides. NOx is a reactive gaseous compound that is one of the criteria air pollutants regulated by the USEPA Clean Air Act. The two primary oxides of nitrogen involved in air pollution are NO and NO2. Nitric oxide (NO) is colorless and essentially odorless. Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent smell. NOx (NO & NO2) can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. NOx is also a precursor to the formation of ground level ozone (smog) and a contributor to acid rain.
  NOx emissions are produced during the combustion of fuels. The primary man-made sources of atmospheric NOx include; area mobile sources (cars and trucks), off-road sources (construction and agricultural machines, trains, etc.) and stationary sources (power plants, industrial boilers & heaters, etc,).
  In a combustion process, three types of NOx can be formed:
  • Thermal NOx, from high temperature combustion in the presence of free oxygen.
  • Fuel NOx – from the nitrogen bound in the fuel when it is oxidized during combustion.
  • Prompt NOx – from the combustion flame and the ambient nitrogen in the ambient air.
Can my 350 be used for compliance testing?
Yes. The testo 350 is used for compliance testing across the country. Testing for regulatory compliance is performed according to approved protocols. The EPA has a variety of methods specifically for electrochemical Analysers, CTM-030, CTM-034, and ASTM designation D 6522-00. Some state and local "air boards" also have "approved" test protocols. We recommend you contact your local regulatory agency to determine which testing protocol best fits your application.
Can I correct my values to an oxygen reference (O2 ref)?
Yes. The testo 350 will automatically calculate, NOx, NO, CO and SO2 to a corrected oxygen reference. The "O2 ref." can easily be changed from 0% to 25%. Regulatory agencies typically require the pollutant gas to be reported to a specific "oxygen reference" to ensure uniformity in the reports. Additionally, this calculation is used to eliminate the consequence of adjusting the controls to subtract or add air to the combustion system thereby changing the ppm reading. Typical oxygen reference levels are: 3% or 7% for boilers and burners, 12% or 15% for engines and turbines.
Can I do long-term monitoring?
Yes. Special design features enable the testo 350 to perform long-term testing. With a huge internal memory (250,000 data points), your testing can go on for weeks if not months. The automatic program has extensive testing capabilities. Start and stop a test on a certain date or for a defined length of time. Simply define the time for sampling, the rate for data logging, and the length of time for the fresh air purge. The Analyser can print the test with a calculated mean average or as single discreet measurements or download to either of testo's software programs.
Can I do 10 minute or 15-minute tests?
Yes. Just define the test program, push the start button, and the Analyser will do all the work. With a huge internal memory, you do not need to have a computer on-site. Testing time, fresh-air time, data logging rate are all user-defined. Data will be automatically saved to any location specified by you. The test data can be printed on site or downloaded to a computer in the comfort of your office.
Questions on Calibration
How often must I calibrate my Analyser?
The short answer is "as often as required". Electrochemical cells in good condition should not drift more than 5% per year. However, as the sensor ages the output diminishes, therefore the calibration frequency may need to be increased. Once or twice per year is usually adequate for most applications. Testing for regulatory purposes will often require a calibration before and after each test. This self-calibration is easily performed with calibration gases.
Questions on Maintenance/Service
What basic maintenance can I perform myself?
  • Particle filters (0554.3381) should be replaced when discolored or obvious particulate buildup occurs. This is a function of usage, frequency and sample conditions.
  • Condensate water should be removed by either attaching a hose to the port on the condensate trap and letting the water drain by gravity or removing the trap from the Analyser Box and shaking the water out.
  • The O-rings on the probe hose barbs should also be checked and replaced as needed.
Can I replace sensors in the field?
Yes! Replacement sensors come from testo pre-calibrated and ready for installation. Most people can install the sensor in less than one minute.
Questions on Software
Do you have any software for the 350 Analyser?
testo offers two different types of software:
easyEmmisions Software
The easyEmissions software package allows the user to control every function of the 350 S/XL. The software provides extraordinary data management capability and the ability to import/export data from a number of different formats, effectively increasing the versatility and flexibility of the 350 S/XL to meet the user's testing and data management needs easyEmission has the intuitive user interface of today's common Windows® based applications. Display screens can be customized to match the most commonly used functions. Prepare custom reports and documents with the powerful data management features.
(i.e. site name, location, measurement, field comment, etc.)
Microsoft Excel® based Import Tool
The simple testo 350 Import Tool lets you use your existing Excel® program to collect real time data or download tests directly into your Excel® spreadsheet. It provides simple operation and only the necessary functions for easy report writing.
General Questions
What can you measure with the 350?
The 350 can measure O2, CO, NO, NO2, SO2, H2S, Hydrocarbons, CO2, pressure, temperature, flow, velocity, current, and rpm.
What sample conditioning is used?
A Peltier cooling system cools the flue gas and condenses the water for removal by an on-board peristaltic pump. The Analyser incorporates a powerful sample pump for high velocity sampling. By combining high velocity sample rates, minimized surface areas, and reduced residence time, the system offers the performance of a stack testing reference system. Heated sample lines and heated hose adaptors are also available for those test methods that require it.
How long will the 350 Analyser operate on battery?
The testo 350 Analysers will operate for 2-3 hours on a single full battery charge. This includes operating a complete sample gas conditioning system and all other Analyser parameters in the portable mode. If needed, an additional battery can be swapped out or an AC power cord connected for longer-term or semi-continuous monitoring.