Features

Sensor

• Compact (sensor head measures 1" x 2" x 3")
• Fast Response - 330 Hz (based on impulse response)
• Low Detection Limit - 50 ppb (propylene in air)
• High Signal-to-Noise Ratio
• Photo-Ionization Detector utilizing RF excited UV lamp
• Robust

Controller

• Analog Output (0 - 10V)
• Real-time Bar-graph Display of the Sensor Output
• Built-in Anti-Aliasing Filter (8th Order Butterworth)
• Easy to Use

Optional Support Equipment

• Calibration Kit
• Data Acquisition System
• Tracer Gas Release System
  
  

miniPID Sensor Head >> Click to enlarge picture

Operating Principle

The miniPID detector is a photo-ionization detector (PID). In the detection cell the 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 miniPID 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 miniPID is dependent on whether interference gases are present.

Optional Support Equipment

Support equipment includes: a manual calibration system, data logging computer, and tracer gas disseminator.

The calibration system consists of a gas-mixing rotometer and control valves which allow calibrated gases to be precisely mixed and delivered to the sensor inlet.

The sensor is designed to interface to any standard data acquisition system (for best results use a 16-bit A/D converter and sampling frequency greater than 1 kHz). Aurora Scientific Inc. can provide a complete data acquisition system on request.

Several tracer gas dissemination systems are available for wind tunnel and outdoor experiments. These range from simple manual systems to remote-controlled systems complete with flow measurement.

Sensor Performance

Frequency Response

The frequency response of a gas sensor can be characterized by either measuring the rise time when the concentration is increased suddenly or by measuring the response to a narrow gas pulse. The miniPID has a measured rise time (10-90%) of 0.5 msec which can be converted to a frequency response of 2000 Hz. A more rigorous method is to fit a Gamma distribution to the impulse response from a narrow gas pulse, compute the power spectrum and then determine the frequency at the -3 db point. When this analysis is performed the miniPID is found to have a frequency response of 330 Hz.

Field Data

Figure 1 shows data from a field trial which was conducted on mud flats near Dugway, Utah. The sensor inlet was set 0.45" (1.14 cm) above ground level, 10 m downwind of the release point. The atmospheric conditions were slightly unstable and the wind speed was 5 m/s. Data was collected with a 16-bit A/D converter at 4000 samples per second.

Figure 1 >> Click to enlarge picture

Figure 2 shows data taken in a University of Utah wind tunnel. The sensor inlet was set 0.45" (1.14 cm) above the tunnel floor, 1 m downwind of the release point and the velocity in the free stream was 3 m/s. Data was collected with a 16-bit A/D converter at 4000 samples per second.

Figure 2 >> Click to enlarge picture

Applications

Field Uses

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

Laboratory Uses

• Wind Tunnel Dispersion Studies
• Wind Tunnel Gas Mixing Studies
• Wind Tunnel Evaporation Studies
• Chemical Defence Chamber Testing

A miniPID sensor in use at Prof. Ring Carde's lab, Dept. of Entomology, University of California, Riverside. The sensor is mounted on a 3-axes positioner built by Paul Stovall and Dan Giles of the Engineering Shop at UCR. >> Click to enlarge picture

The miniPID sensor can be customized to meet your research needs. Custom features include: sample flow rate, inlet length and geometry, cut-off frequency of the anti-aliasing filter, concentration range, location of sample pump (in controller or sensor head), sensor head mounting method, rack-mounted controllers for multiple-sensor applications, scanning valve for multi-point measurements, and built-in A/D converter with microprocessor for direct connection to a computer. Contact Aurora Scientific Inc. with your specific requirements.

miniPID Specifications

• Detector Technology: Photoionization, with 10.6 eV RF-excited electrodeless discharge tube
• Frequency Response: 330 Hz (@ the -3 dB point)
• Detection Limit: 50 ppb (propylene)
• Operating Concentration Ranges: Low Gain: 0 - 1000 ppm, Med Gain: 0 - 200 ppm, High Gain: 0 - 40 ppm
• Precision: 5.0% (all gain ranges)
• Sampling Rate: 1.1 litres/minute
• Operating Humidity Range: 0 to 100% RH (non-condensing)
• Operating Temperature Range: 32F to 105F (0C to 40C)
  

Dimensions

• Sensor Head: 3.0" (7.6 cm) long, 2.0" (5.1 cm) wide, 1.0" (2.5 cm) thick.
• Controller: 5.25" (13.3 cm) long, 5.25" (13.3 cm) wide, 2" (5.1 cm) high.

Weight

• Sensor Head: 0.38 lbs (0.17 kg).
• Controller: 1.47 lbs (0.67 kg).

Power: 110/220VAC, 50/60 Hz.

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.