General Questions

Can I buy direct from testo?

Testo products can be purchased through our distribution network.  To find your nearest distributor click here.

Questions About Gas Sensors

Are the sensors temperature compensated?

Yes. Most electrochemical analyzers use temperature compensation to eliminate drift due to temperature change. Analyzers typically base their compensation on the temperature when the analyzer is first turned on. The sensor output will remain linear within a limited temperature range depending upon the analyzer and sensor configuration. The testo 350 utilizes continuous temperature compensation and sensor temperature control to ensure accuracy. Integrated circuit boards on each sensor provide the mechanism to apply a continuous temperature compensation curve 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 20º F.

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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 the 330-2, 335 and 350 sensors. 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 analyzer to the factory.

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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 analyzer 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.

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How are sensors protected?

The analyzer 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 analyzer is turned off it will go through a shut-down sequence that purges residual gases from the analyzer resulting in longer sensor life and more stable output.

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What is a CO dilution system?

The dilution system extends the range of the CO sensor by a factor of 40 times. The analyzer 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.

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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. To view the chart click here.

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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 (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.