Features

Sensor

• Fast Response - 50 Hz
• Low Detection Limit - 40 ppb (propylene in air)
• High Signal-to-Noise Ratio
• Built-in 20-bit Analog-to-Digital Converter
• Microprocessor Controlled with Built-in RS-232 and RS-485 Interfaces
• Photo-Ionization Detector utilizing RF excited UV lamp
• Robust

Control Software

• Controls and Logs Data from up to 16 Sensors
• Real-time Graphical Display of Incoming Data
• Menu Driven, Easy to Use
• DOS Program, requires i486 or better CPU
• Microprocessor Controlled with Built-in RS-232 and RS-485 Interfaces
• Photo-Ionization Detector utilizing RF excited UV lamp
• Robust

Optional Support Equipment

• Calibration Kits
• Data Acquisition Computer Systems
• Tracer Gas Release Systems

Operating Principle

The digitalPID detector is a photo-ionization detector (PID). In the detection cell a gas or vapour sample is exposed to high intensity ultraviolet light which ionizes the molecules of chemical substances. Ions are collected on positive and negative electrodes within the detector cell, creating a current proportional to the contaminant concentration. Ionization depends on the minimum energy needed by a molecule to produce ions and this energy (ionization potential) is different for each chemical substance. The molecules of most permanent gases (including the constituents of air: nitrogen, oxygen, carbon dioxide, argon, etc.) are not ionized as they require a photon energy level higher than that generated by the lamp. Molecules having ionization energy levels below the lamp energy (10.6 eV) are the ones that are ionized.

Since the digitalPID is sensitive to any gas with an ionization potential below 10.6 eV, the output of the device should be viewed as an expression of the total ionizables present. Because of this, the accuracy of the digitalPID is dependent on whether interference gases are present.

Optional Support Equipment

Optional support equipment includes calibration systems, PC-based data acquisition systems and tracer gas disseminators.

1. Two calibration systems are available: a manual kit which consists of calibrated gas mixtures along with flow regulators packed in a brief-case size carrying case, or a computer controlled calibration system capable of simultaneously calibrating up to 16 sensors. The control software (included with the sensor) has provisions for both manual and computer controlled sensor calibration.
2. Complete PC-based data acquisition systems which range from laptop to rack-mounted are available.
3. Several tracer gas dissemination systems are available for either wind tunnel or outdoor experiments. These range from simple manual systems to remote-controlled systems complete with flow measurement. Disseminators for short duration or "puff" releases are also available.

The digitalPID sensor provides un-aliased data at 50 Hz. This is achieved by having a detection cell frequency response in excess of 150 Hz, and by using an integrating analog-to-digital converter (ADC) which operates at a minimum frequency of 125 Hz and then averages multiple samples to provide output at a rate of 50 samples per second.

Field Data

Figure 1 shows data from the SCIPUFF validation trials that took place on mudflats near Dugway, Utah. The tracer was propylene and it was released as an explosive "puff". The sensor was located 1.5 m above ground level, 356 m downwind of the release point. The atmospheric conditions were neutral and the average wind speed was 4.6 m/s at 2 m above ground level and 5.4 m/s at 8 m above ground level.

Figure 1 >> Click to enlarge picture

Applications

Field Uses

• Dispersion Studies (CONFLUX)
• Model Validation (SCIPUFF)
• Tracer for Biological Simulants (BIDS, JFT, ACTD)
• Evaporation Studies
• Heavy Gas Studies (GRADE)
• Building Infiltration Studies

Laboratory Uses

• Indoor Gas Dispersion Studies (building infiltration and contaminant movement)
• Wind Tunnel Gas Mixing or Evaporation Studies
• Chemical Defence Chamber Testing

Custom Sensor Configurations

The digitalPID sensor can be customized to meet your research needs. Custom features include: sample flow rate, inlet length and geometry, concentration range, mounting method, rack-mounted or laptop data acquisition computers, wireless data transmission systems, and scanning valves for multi-point measurements. Contact Aurora Scientific with your specific requirements.

Fluctuation Analysis Software

A fluctuation analysis (FAN) software package is available for the efficient analysis of large data sets. The program is written in ANSI C and may be compiled to run on any 32-bit computer. Full details of FAN are available on request. Aurora Scientific Inc. also provides data analysis services.

digitalPID Specifications

• Detector Technology: Photoionization, with 10.6 eV RF-excited electrodeless discharge tube.
• Frequency Response: 50 Hz.
• Detection Limit: 40 ppb (propylene).
• Operating Concentration Ranges: Gain 1: 0 - 800 ppm, Gain 2: 0 - 200 ppm, Gain 3: 0 - 50 ppm, Gain 4: 0 - 25 ppm
• Precision: 5.0% (all gain ranges).
• Air Sampling Rate: 1.0 litres/minute.
• A/D Converter: 20-bit precision, wide dynamic range, charge digitizing.
• Communications: RS-232 or RS-485.
• Operating Humidity Range: 0 to 100% RH (non-condensing).
• Operating Temperature Range: 32F to 105 (0C to 40C).
• Enclosure: Anodized aluminum.
• Dimensions: 2.0" (5.1 cm) high, 3.0" (7.6 cm) wide, 8.75" (22.2 cm) long.
• Weight: 2.25 lbs (1.0 kg).
• Power: 1.5A @ 12VDC.

References

The following are open-literature papers describing data and data analysis obtained using miniPID or digitalPID detectors in full-scale field trials.

miniPID and digitalPID References.