NDIR VS Solid States
Solid State vs Non-dispersive Infrared Refrigerant Gas Sensors
For many refrigeration applications, using solid state sensors will provide an economical and reliable gas detection solution. Solid state sensors are reliable if used in a clean area with very little temperature and humidity changes. Solid State refrigerant sensors should not be used where there are other chemicals or gases present (other than refrigerants), such as alcohol based cleaners, fumes from running engines, fuel storage containers, etc.
Using infrared sensor technology will ensure the highest degree of sensor accuracy if monitoring an area where there are other contamination gases or multiple refrigerants in the same area. Infrared refrigerant sensors should not be used in locations that have corrosive chemicals such as chlorine, ammonia and other oxidizers that are present, especially if there is a higher humidity level.
Comparison of CET’s Solid State Refrigerant Sensors and Infrared Refrigerant Sensors
| Solid State Refrigerant Sensors | Non-dispersive Infrared Refrigerant Sensors | |
| Mode of Operation | Metal oxide changes resistance in response to the presence of target gas. The change is measured by the electronics of the detector to determine the gas concentration. | Gas molecules absorb the infrared light of the optical sensor at a certain wave length. The wave length is measured by the electronics of the detector to determine the gas concentration. |
| Specific Refrigerant Gases Detected in CETCI Gas Detectors | R22, R134A, R402A, R404A, R407C, R410A, R422D, R438A, R507A | R22, R32, R123, R134A, R404A, R407A, R407C, R407F, R410A, R427A, R448A, R449A, R507, R422A, R422A, R452A, R513A, HFO1234YF, HFO1234ZE, FO1233ZD |
| Output | Non-linear | Linearized |
| Gas Detection Range (gas dependant) | 0 – 2,000 ppm | 0 – 3,500 ppm (0 – 1,000 ppm for R123) |
| Sampling Method | Diffusion | Diffusion |
| Life Expectancy | 5 to 7 years | 7 to 10 years |
| Maintenance | Low | Low |
| Calibration | Less calibration frequency required, every 12 months recommended. |
Establish and maintain zero point and the accuracy of the detector remains intact. Less calibration frequency required, every 12 months recommended. |
| Sensitivity | High, detects low gas concentrations | High, detects low gas concentrations |
|
Accuracy (gas dependent) |
±15% | ±5% (if calibrated to specific refrigerant) |
| Response Time T90 | < 2 minutes (target refrigerant dependent) | < 5 minutes |
| Drifting/Aging | Susceptible to temperature and humidity changes, require regular calibration to compensate for drift/aging | Less susceptible to temperature and humidity changes, little drift, moderate aging |
| Operating Temperature | -20°C to 40°C (-4°F to 104°F) | -30°C to 40°C (-22°F to 104°F) |
| Response to Temperature Changes | Sensitive to changes in temperature | Short term response to large changes in temperature |
| Operating Relative Humidity | 15 - 90% RH non-condensing | 5 - 90% RH non-condensing |
| Response to RH Changes | Sensitive to changes in humidity | High humidity can affect response and promote corrosion. |
| Wet Environments | Will shorten lifespan | Water or vapour condensation can impair the optics ability to function. |
| Dry Environments | Must be calibrated in the environment it will be operating in. | No problem in dry environments |
| Dirty, Dusty Environments | Will shorten lifespan and requires calibration more often. | Dust and dirt can coat the optics and impair the sensor response. |
| Time Required to Stabilize | New sensor is stable after 3 minutes; old sensor (ie. 5 yrs) may take 5 minutes. | Typically requires 10 to 20 minutes to equalize after a sudden variation in temperature. May take up to 30 minutes to stabilize from a change in humidity. |
| Presence/Absence of Oxygen (Air) | Requires oxygen for proper functioning. | No minimum level of oxygen required; operates in the absence of, or enriched presence of oxygen. |
| Cross Contamination | Non-specific, sensitive to many other gases, vapours and chemicals, susceptible to false alarms | Can be configured for broad range or gas specific, few false alarms. Cross sensitivity to other refrigerants. |
| Exposure to High Concentrations of Gas (poisoning) | Moderately resistant to poisoning | Will not burnout, immune to poisoning. May require a long time to clear before accurate readings can be taken again. |
| Continuous Exposure to Gas | Sensor reading will become unreliable after 15 minutes (will read higher than calibrated value). | Does not affect operation |
| Power Consumption | High | High |
| Cost | Economical | Can be expensive |
Applications for Refrigerant Sensors: Recommendation by Sensor Type
| Application | Sensor Type | Reason |
| Boiler / Machinery Rooms | IR | No false alarms, longer life span, less maintenance |
| Breweries | IR | No false alarms, longer life span, less maintenance |
| Chiller Rooms | IR | No false alarms, longer life span, less maintenance |
| Convenience Stores | SS | IR too expensive |
| Hotels | SS | Requires a small remote sensor on a cable for rooms with air conditioners |
| Shopping Malls | IR | No false alarms, longer life span, less maintenance |
| Supermarkets | IR | No false alarms, longer life span, less maintenance |
| Universities | IR | No false alarms, longer life span, less maintenance |
| Office Buildings | IR | No false alarms, longer life span, less maintenance |
| Hospitals | IR | No false alarms, longer life span, less maintenance |
NOTE: Ammonia is commonly used as a refrigerant in very low temperature applications such as food/meat processing, ice making plants and ice arenas. Electrochemical sensors are required to ensure accurate monitoring in Ammonia applications.
