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manuel de l'hygromètre OptiSonde chilled mirror

détails et spécifications techniques de l'OptiSonde

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OptiSonde™
Chilled mirror hygrometer

Key benefits

Patented PACER® cycle automatically cleans mirror to ensure measurement integrity
Chilled mirror hygrometers are used in standards and metrology labs as well as in industrial applications where precise and repeatable humidity measurement and control are required.
The inherent accuracy and long-term stability provide many advantages over other types of humidity measurement technologies.
Compact and rugged design for easy installation and durability
Built-in data logger provides ability to record historical data
Sensor conveniently plugs into wall mount chassis for facility monitoring, eliminating the need to run cable
Sensors may be connected up to 91 m away via cable for remote monitoring
Displays and transmits in a variety of parameters, such as dew point, relative humidity, dry bulb, wet bulb, absolute humidity, volume ratio, and mass ratio, offering flexibility during operation
Digital (RS-232) interface for data integrity

The OptiSonde chilled mirror hygrometer is a National Institute of Standards and Technology (NIST) traceable humidity transfer standard at an exceptional value. The compact rugged analyzer is connected to either a single-or two-stage chilled mirror sensor and PRTD. Chilled mirrors are the humidity sensors of choice when laboratory and process measurements require high precision without long-term drift. An LCD indicates two simultaneous user-configured parameters. OptiSonde provides two user-configured analog (4 to 20 mA) outputs. The display and front panel keys enable quick and easy configuration.

Applications

Environmental test chambers
Engine test cells
Clean rooms
Air conditioning and heat exchange coil testing
Metrology labs

Theory of operation

Chilled mirrors fundamentally measure the dew or frost point temperature by controlling a reflective surface to an equilibrium temperature between dew/frost formation and evaporation and precisely measuring the temperature of the mirror at this point. The chilled mirror sensors consist of a small polished hexagonal rhodium, or platinum mirror attached to a thermoelectric cooling module (TEC). OptiSonde’s servo controller applies current to the TEC, which causes the mirror to cool. The mirror is illuminated with a regulated Gallium Arsenide (GaAs) emitter that transmits light in the infrared spectrum. The light reflected by the mirror is received by a photo detector. When water vapor condenses on the mirror as water or frost (ice crystals), the light received by the photodetector is reduced due to scattering. This results in the servo controller reducing the power, causing the mirror to slightly warm. OptiSonde’s control system will modulate the amount of current flowing though the TEC to maintain a temperature where the rate of condensation and evaporation of water molecules and the mass of water on the mirror are constant. The resulting temperature of the mirror is then, by definition, equal to the dew or frost point temperature. A precision four-wire platinum RTD embedded in the mirror measures the temperature. The accuracy of the dew point measurement has been validated to an accuracy of ±0.2°C dew/frost point.

Contamination control and self-cleaning mirrors

For environments where physical contaminants such as dust, oil mist and pollen are present, the use of a sampling system with a filter media is recommended. The filter media must be hydrophobic so as to not absorb or release water vapor into the test stream. Over time the mirror can be etched or pitted by particulates that lead to altering the light scattering characteristics. The mirrors are field replaceable. The standard rhodium mirror may be upgraded to platinum for industrial applications. The two-stage sensors also utilize stainless steel wetted surfaces. PACER® (Program Automatic Error Reduction) is a patented contamination compensation scheme. The PACER cycle may be initiated manually or by programming a timed cycle. The cycle starts by capturing the data (during the PACER cycle a constant reading can be transmitted via the analog outputs) and cooling the mirror well below the dew point such that a thick dew layer forms on the mirror. The mirror is then rapidly heated. During the heating a significant amount of soluble and some non-soluble contamination is flash evaporated. The contamination left on the mirror tends to aggregate in “dry islands” or “spots” (much like a glass that comes out of a dishwasher). This process leaves approximately 85% of the mirror clean. The light signal received by the photodetector is compared against a reference LED/photodetector and the two signals are “balanced,” effectively negating the effect of the residual contamination left on the mirror.

Calibration services

Proper calibration is critical to the measurement integrity of your equipment. Comparing and adjusting the output of a device or sensor against a known reference standard ensures accuracy, reliability and repeatability. We provide a single source for initial start-up, programming and verification, and for scheduled calibrations. The requirements of your application dictate the frequency of calibration and we will tailor a multi-year contract to your needs. We perform on-site calibrations that keep your equipment in your facility—minimizing downtime. This is a good alternative if you have more than one piece of equipment. Mail-in service to our modern calibration facilities provides a more controlled environment and NIST traceability.

OptiSonde specifications

Temperature accuracy: ±0.15°C
Repeatability: 0.05°C
Display: Two simultaneous parameters with 0.01°C resolution. “Dew Layer Thickness,” “Control,” “Alarm” and “Service” indicators.
Analog Output: Two linear simultaneous parameters. 0/4 to 20 mA (isolated) with 250? max load
Alarm: Form C (SPDT) 7 amp, 30 VDC (resistive load)
Digital interface: RS-232
Cooling Slew Rate: 1.5°C/sec
Self Cleaning and Balancing: Via patented PACER cycle. PACER may be programmed to run on an elapsed time or daily timer.
Operating temperature: Analyzer: -10°C to 60°C
Data Logger: Capable of recording eight parameters, time, and date for a minimum of 100 days at sample rate of one second.
Operating humidity: 0 to 95% RH non-condensing
MTBF: Five years of continuous operation
Certifications: CE Approval
Power: • 100 - 240 VAC, 50 to 60 Hz, 60 watts • 18-32 VDC (bench top only)
Enclosure Material: • Wall mount: Cast aluminum • Bench top: Aluminum body with plastic front bezel
Dimensions: • Wall mount: 26.6 x 20.8 x 11.4 cm (h x w x d) • Bench top: 9.4 x 20.3 x 22.4 cm (h x w x d)
Weight: • Wall mount: 2.4 kg • Bench mount: 1.4 kg
Ingress protection rating: • Wall mount: IP-65 • Bench top: IP-20
Front panel keys: • Rubber function keys—may be locked out via software
Dew point range — Dependent on sensor used
Dew point accuracy: ± 0.2°C dew/frost point
Dew point repeatability: 0.1°C

Panametrics, a Baker Hughes business, provides solutions in the toughest applications and environments for moisture, oxygen, liquid, and gas flow measurement. Experts in flare management, Panametrics technology also reduces flare emissions and optimizes performance. With a reach that extends across the globe, Panametrics’ critical measurement solutions and flare emissions management are enabling customers to drive efficiency and achieve carbon reduction targets across critical industries including: Oil & Gas; Energy; Healthcare; Water and Wastewater; Chemical Processing; Food & Beverage and many others.