We are often asked about how to properly take CO measurements here at Testo. So we decided to make a video demonstrating how CO measurements can be affected by naturally-occurring NOx.
To learn more about the complete line of Testo's combustion analyzers, check out www.testoUSA.com/combustion.
Thursday, March 28, 2013
Friday, March 22, 2013
Combustion analysis and why CO readings are not always correct
Have you ever compared your CO readings to another analyzer? You might have noticed that Testo CO reading is lower than expected. Why such a difference? The secret lies in the Testo’s addition of the NOx gas filter.
In residential and light commercial combustion analysis there are several important combustion gases that are measured or monitored. Carbon monoxide (CO), however, is arguably the one gas with the most liability associated with it. This is due to safety concerns and simply from the standpoint of good combustion performance. But NOx is also present and can affect the CO readings, it’s the carbon monoxide levels that you just tested that will keep you up at night.
While performing a combustion test, the O2 and CO are right in front of you on the analyzer display, but it’s easy to overlook all the other gases flowing through the flue pipe, like CO2, nitrogen, NOx, SO2, water vapor, and so on. It’s these other gases that need to be accounted for when testing furnaces, boilers heaters and other combustion sources. Why, you ask are these other gases important? Some of them can change the output of sensors, and it’s important to know this when you have critical decisions or combustion adjustments to make. This way you are making them based on good information.
How Electrochemical Sensors Function
Electrochemical (EC) sensors rely on the chemical reaction between the combustion gases and the chemicals/materials inside the sensor. As the targeted gas, (i.e., CO) comes in contact with the sensor materials, a reaction takes place. Specifically, between the metal electrodes and chemicals which in-turn will create an electrical output. Technically speaking, this process is call a redox reaction (oxidation or reduction) depending upon the sensor. When the flue gas component (i.e., CO) is no longer present, the chemical reaction and electrical output stops.
The technology behind an EC sensor is well established and is designed to detect both low and high levels of a specific gas through different sensor designs and materials. The key to a quality EC sensor is its’ ability to isolate a single measurement parameter while remaining unaffected by the wide range of other components in the flue gases.
How NOx Affects CO Sensor Readings
If a sensor within a combustion analyzer responds to gases other than what it’s intended to measure, an incorrect measurement will be displayed. This will occur when a CO sensor - without a NOx scrubbing filter - is exposed to flue gas. All flue gas contains some concentration of NOx (for simplification, NOx refers to Nitrogen Oxide). The concentration of NOx tends to be higher with elevated temperatures and low O2 concentrations. When NOx enters the CO sensor, additional reactions take place that increase sensor output. It is impossible to know how much of the output is due to CO and how much is the result of NOx.
Many government weatherization programs and performance testing guidelines require corrective action when specific levels of CO are detected. This can prove to be time consuming and costly when these corrective actions are based on potentially false CO readings.
CO Sensor Design
The design of a CO sensor should include a way to eliminate the cross interference effect to other flue gases, namely Nitrous Oxide (NO). If the CO sensor is designed incorrectly, the CO measurement will be wrong. For example, if the CO sensor is exposed to flue gas containing 100ppm CO and 200ppm NO (remember NO may not be displayed or measured on the combustion analyzer), the CO sensor will react with a positive output for CO and an additional positive output for the NO. As such, the CO sensor will calculate 100ppm of CO and also calculate an additional 50-100ppm of NO, resulting in a displayed value of CO as much as 200ppm. As a result, technicians will attempt to mechanically correct the burner to lower CO levels. The correction will be wrong and will negatively impact burner/system performance.
Testo’s Sensor Design
For decades, Testo has used CO sensors with integrated NOx filters as a standard design. These filters “scrub” and remove NOx from the gas stream. Ultimately, this prevents NOx from ever reaching the CO sensor. This NOx filter is designed to last longer than the life of the sensor so there is no maintenance required when used under normal operating conditions. In some of Testo’s analyzers the filters can be replaced in the field. Go to http://www.testousa.com/combustion/ to see more of Testo’s line of combustion analyzers.
Confidence in Testo Sensors
Filtering NOx from the combustion gas stream before it goes through the sensor is fundamental to achieving accurate CO readings. Without a NOx filter the validity of the CO reading will always be in question.
If there is ever a concern in your CO readings, it’s easy to confirm proper function by using calibration gas. Connect and flow NO calibration gas to your analyzer. The CO sensor should show 0ppm. If a filter is not present, expect to see a 25%, to over 100%, value of the NOx gas in your CO reading. Although this procedure is easy to do, most contractors don’t carry calibration gas. So to eliminate the questions, use the proper sensor, and analyzer for accurate combustion testing.
In residential and light commercial combustion analysis there are several important combustion gases that are measured or monitored. Carbon monoxide (CO), however, is arguably the one gas with the most liability associated with it. This is due to safety concerns and simply from the standpoint of good combustion performance. But NOx is also present and can affect the CO readings, it’s the carbon monoxide levels that you just tested that will keep you up at night.
While performing a combustion test, the O2 and CO are right in front of you on the analyzer display, but it’s easy to overlook all the other gases flowing through the flue pipe, like CO2, nitrogen, NOx, SO2, water vapor, and so on. It’s these other gases that need to be accounted for when testing furnaces, boilers heaters and other combustion sources. Why, you ask are these other gases important? Some of them can change the output of sensors, and it’s important to know this when you have critical decisions or combustion adjustments to make. This way you are making them based on good information.
How Electrochemical Sensors Function
Electrochemical (EC) sensors rely on the chemical reaction between the combustion gases and the chemicals/materials inside the sensor. As the targeted gas, (i.e., CO) comes in contact with the sensor materials, a reaction takes place. Specifically, between the metal electrodes and chemicals which in-turn will create an electrical output. Technically speaking, this process is call a redox reaction (oxidation or reduction) depending upon the sensor. When the flue gas component (i.e., CO) is no longer present, the chemical reaction and electrical output stops.
The technology behind an EC sensor is well established and is designed to detect both low and high levels of a specific gas through different sensor designs and materials. The key to a quality EC sensor is its’ ability to isolate a single measurement parameter while remaining unaffected by the wide range of other components in the flue gases.
How NOx Affects CO Sensor Readings
If a sensor within a combustion analyzer responds to gases other than what it’s intended to measure, an incorrect measurement will be displayed. This will occur when a CO sensor - without a NOx scrubbing filter - is exposed to flue gas. All flue gas contains some concentration of NOx (for simplification, NOx refers to Nitrogen Oxide). The concentration of NOx tends to be higher with elevated temperatures and low O2 concentrations. When NOx enters the CO sensor, additional reactions take place that increase sensor output. It is impossible to know how much of the output is due to CO and how much is the result of NOx.
Many government weatherization programs and performance testing guidelines require corrective action when specific levels of CO are detected. This can prove to be time consuming and costly when these corrective actions are based on potentially false CO readings.
CO Sensor Design
The design of a CO sensor should include a way to eliminate the cross interference effect to other flue gases, namely Nitrous Oxide (NO). If the CO sensor is designed incorrectly, the CO measurement will be wrong. For example, if the CO sensor is exposed to flue gas containing 100ppm CO and 200ppm NO (remember NO may not be displayed or measured on the combustion analyzer), the CO sensor will react with a positive output for CO and an additional positive output for the NO. As such, the CO sensor will calculate 100ppm of CO and also calculate an additional 50-100ppm of NO, resulting in a displayed value of CO as much as 200ppm. As a result, technicians will attempt to mechanically correct the burner to lower CO levels. The correction will be wrong and will negatively impact burner/system performance.
Testo’s Sensor Design
For decades, Testo has used CO sensors with integrated NOx filters as a standard design. These filters “scrub” and remove NOx from the gas stream. Ultimately, this prevents NOx from ever reaching the CO sensor. This NOx filter is designed to last longer than the life of the sensor so there is no maintenance required when used under normal operating conditions. In some of Testo’s analyzers the filters can be replaced in the field. Go to http://www.testousa.com/combustion/ to see more of Testo’s line of combustion analyzers.
Confidence in Testo Sensors
Filtering NOx from the combustion gas stream before it goes through the sensor is fundamental to achieving accurate CO readings. Without a NOx filter the validity of the CO reading will always be in question.
If there is ever a concern in your CO readings, it’s easy to confirm proper function by using calibration gas. Connect and flow NO calibration gas to your analyzer. The CO sensor should show 0ppm. If a filter is not present, expect to see a 25%, to over 100%, value of the NOx gas in your CO reading. Although this procedure is easy to do, most contractors don’t carry calibration gas. So to eliminate the questions, use the proper sensor, and analyzer for accurate combustion testing.
Thursday, March 21, 2013
Video of the new testo 552 digital vacuum gauge
Here is a video discussing all the features and benefits of the all new testo 552 digital vacuum gauge.
For more information about the new testo 552 digital vacuum gauge, check out www.testousa.com/refrigeration.
For more information about the new testo 552 digital vacuum gauge, check out www.testousa.com/refrigeration.
Tuesday, March 12, 2013
Testo Introduces Maintenance-Free Vacuum Gauge
Testo Inc., world leader in the design, development and manufacture of portable instrumentation, introduces the new testo 552 Digital Vacuum Gauge to confirm the evacuation of air conditioning, heat pump and refrigeration systems. Unlike other vacuum gauges, the testo 552 requires no cleaning, nor is it susceptible to contamination from oils. Aside from this big time savings benefit, the absolute pressure sensor delivers fantastic accuracy to +/-10 microns. You can count on reliable readings every time.Outfitted with a large back-lit display, and rugged IP 42 Protection Class (dust & splash resistant) housing, the testo 552 is tough enough to withstand a 6 foot drop. Additional features include long battery life to 2400 hours, a high limit alarm, and display of water evaporation temperature. For owners of the testo 570 Digital Manifold, the testo 552 can be connected to the t570 to data log and/ or print your evacuation data.
John Bickers, Director of Product Management, adds, “The industry has been looking for a no clean, no maintenance vacuum gauge that they can count on, we are very happy to answer with the testo 552.”
Monday, March 11, 2013
Testo 320 Residential & Light Commercial Combustion Analyzer
Here is a video about one of Testo's latest instruments - the testo 320 residential and light commercial combustion analyzer.
Thursday, March 7, 2013
Testo 310 Residential Combustion Analyzer Video
Here is a video about one of Testo's latest instruments - the testo 310 residential combustion analyzer.
Wednesday, March 6, 2013
Enter Testo's Ultimate Contractor Giveaway!
Testo products included in the giveaway include:
- testo 875i-1 thermal imager
- testo 570 digital manifold
- testo 435 HVAC performance test kit
- testo 320 combustion analyzer
Features of the 875i-1:
- 160 x 120 resolution
- 50 mK sensitivity
- Visual camera
- 32 degree wide angle lens
- IRSoft reporting software
Features of the 570 digital manifold:
- 4-way valve block
- Two external temperature probes
- Heat pump mode
- Automatically collect and store data for up to 99 hours
- Calculate superheat and subcooling simultaneously, in real time
- Time-saving programmable functions
- Four-function IAQ probe
- Integrated differential pressure measurement
- Data recording up to 10,000 readings
- PC software for analyzing, archiving, and documenting
- Wireless or cabled humidity probes
Features of the testo 320:
- Draft and pressure measurement
- Gas leak detection
- Ambient CO measurement
- Cam-lock fittings
- Long-lasting sensors
Only one entry per person
- No Purchase is required
- Open only to contractors residing in North America
- Survey and giveaway entries will close on May 31, 2013
- Winner will be notified by email and posted on website www.testoUSA.com
- Employees of Testo along with distribution and wholesale partners and any family members are not eligible to participate in the giveaway.
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