Manuals - Bulletins - Drawings
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
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 miniPID is the fastest gas sensor on the market that can accurately monitor and quantify the concentration of an input gas or vapour.
Rise time = 0.65 milliseconds (1-99%)
Fall time = 1.32 milliseconds (99-1%)
Frequency Response = 330 Hz.
Click to enlarge picture
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.