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Comparative analysis of counting technologies

From active electro-optics to thermal to beams, each technology has its benefits, ideal usage and downsides. Learn more on this high-tech subject.

There are many different technologies available in the people counting industry. However, not all are suitable for the outside environment and some are simply unreliable and ineffective. We will discuss each technology one at a time.

Infodev hyas explored different types of sensing technologies such as passive thermal, active infrared, digital cameras or thermal imaging, ultrasound, light beams, etc. We install cameras and passive infrared sensors for applications that involve counting people in interior environments, and active infrared sensors in outside environments. We chose not to create dual technology type sensors because our active infrared technology, at its advanced status, is highly accurate.

  • Comparative summary
  • Passive thermal directional sensors
  • Active infrared directional sensors
  • Passive infrared directional sensors
  • Passive infrared presence detector
  • Light beams
  • Dual technology sensors
  • Camera-based technologies

SUMMARY

 

Technology

 

 

Strengths

 

 

Weaknesses

 

Passive thermal

Will not count objects or anything else that is not human body temperature.
Non-intrusive.

Affected by sudden temperature and light changes.
Blind in warm environments.
Affected by immobile passengers/persons.

Active infrared

Unaffected by sudden temperature and light changes.
Unaffected by immobile passengers.
Highly accurate.
Array installation permits covering wide entrances.
Non-intrusive.

Will not count children under 2,5 ft. tall.

Passive infrared

Adjustable sensitivity increases accuracy.
Array installation permits covering wide entrances.
Non-intrusive.

Affected by changes in the background.

Presence detector

Low cost.
Non-intrusive.

Not directional.
May induce false counts from background noise and nuisance stimuli.

Light beams

Low cost.
Non-intrusive.

Limited detection zone.
Blind spots can let someone pass without being detected.
Require an unobstructed detection zone.

Dual technologies

One technology compensates for the other's weaknesses.
Non-intrusive.

May cause extra counts when both technologies detect a person.

Cameras

May work as a surveillance tool.
Non-intrusive.

Affected by vibrations and changes in light, height, and temperature.
Image quality influences accuracy of processing.
Expensive.

Tread mats

Non-intrusive.

Prone to damage from elements.
Expensive installation and customization.
Unreliable in entrances without steps.

PASSIVE THERMAL DIRECTIONAL SENSORS

The passive detector works by detecting a signal generated by an object, in our case, a human. The signal is invisible infrared light emitted by a body at a finite temperature. The intensity of the emitted thermal radiation increases with the body temperature but it is also affected by the material and surface texture of the object.

When a human goes into the field of view of a passive thermal detector, there is first a reduction of the background caused by the person's opacity and secondly a new source of radiation as the human enters the field. Since the body temperature is usually higher than the surrounding environment, the result is an increase in the infrared light captured by the detector. In short, it looks at the temperature difference between a human and his background.

There are inherent weaknesses of this technology. If the external temperature and the body temperature are similar, the sensor is blind. When a person stands under sensor for some time, he becomes the background and the sensor is blind. Passive thermal sensors are sensitive to quick temperature changes and strong sunlight.

Therefore, we only install passive thermal sensors in interior environments where light and heat conditions can be controlled. We do not recommend this technology for vehicles.

ACTIVE INFRARED DIRECTIONAL SENSORS

Infodev's active infrared technology works within a wavelength of 950 nm. It is different from passive thermal infrared, which works with a wavelength under 10 000 nm. The sensor emits a light source and detects the retro diffused light from a human.

Since the sensor has its own light source, it is not influenced by the external temperature, external light conditions or if people are standing under the sensor, which is common when passengers are waiting in line to purchase a ticket. Active infrared is classified as the most suitable technology to use in external environments.

Moreover, using our specialized algorithms, it is possible to install this sensor in an array to cover wide entrances.

As Infodev specializes in optics technology, our active infrared sensors have a defined height, thickness and angle we wish to cover as a zone, as opposed to other manufacturers who provide just a simple beam. To see more specifications on the performance of our sensors, please request our accuracy report.

We recommend using our active infrared sensors for vehicles, since it is the sturdiest sensor available. We also recommend this technology for building entrances that have important light variations or locations that will be exposed to the elements.

PASSIVE INFRARED DIRECTIONAL SENSORS

Passive infrared directional sensors detect the change in luminosity in the field of vision when someone passes through. If the contrast and length of the change is within parameters, a person is counted and its direction determined.

If an object such as a stroller or shopping cart passes through the sensor's field of view, they might be counted as a person. However, detection parameters permit adjusting the sensor's sensitivity to count only humans.

Moreover, using our specialized algorithms, it is possible to install this sensor in an array to cover wide entrances.

Passive infrared directional sensors may also count incorrectly when there are changes in the background.

We recommend using Infodev's passive infrared directional sensors in building entrances that are not experiencing drastic light changes during the day.

PASSIVE INFRARED PRESENCE DETECTORS

Presence or motion detectors are most common in alarm or security systems. They will only react to changes or motions in the field of view.

Besides not being directional, their main problem is that they can induce false counts from background noise and nuisance stimuli.

Passive infrared systems are also suitable for use as triggers for external cameras.

We don't recommend using this type of sensor to count people.

LIGHT BEAMS

This type of detector acts as a presence sensor that can be installed vertically or horizontally. A light beam is captured by a receiver. The interruption of the light beam by an object indicates that there is something or someone between the light source and the detector.

Active infrared beams count a person when he or she crosses their field of vision.

Though many suppliers have claimed that their active infrared sensor has high accuracy, the beam type is not as accurate as it seems. Beam type technologies, unlike Infodev's sensors that have a defined field of vision, are limited in their detection zone and require an unobstructed path between the transmitter and the receiver. Since the traffic pattern of passengers is random, a person can walk through an entrance but not in the direct view of the sensor and is therefore undetected.

Furthermore, for most of these detectors, direct sunlight exposure will blind the detector and cause lost counts.

This factor then creates enormous errors in the system.

Although their cost is very low, we don't believe these people counters are reliable or accurate.

DUAL TECHNOLOGY SENSORS

Dual technology was introduced because of the inherent weaknesses of the passive thermal technology. In order to reduce the errors generated from passive thermal sensors, suppliers add on an active infrared component to compensate the errors derived from the passive thermal technologies.

Dual technology sensors do not necessarily reduce the error as it may be claimed. They need to know exactly which counts to consider when both sensors are being activated at the same time.

CAMERA-BASED TECHNOLOGIES

Camera-based counting systems image the entrance or part of the entrance. The sequence of images is analysed using software to identify people and track their movement.

The quality of the optical components, the processing power needed to analyse the images and the development cost of the image analysis software all contribute to the relatively high cost of these systems compared to other alternatives.

Cameras are widely used in interior environments, but not in external operating environments. They are highly sensitive to any light variation (switching from day time to night time). When there is a lot of light in a monitored entrance (which is the case of a vehicle), cameras cannot record images accurately and this leads to difficult and sometimes inaccurate image processing at the other end.

Vibrations can displace the camera lens resulting in inaccurate counts and the need for frequent service calls. In certain cases, even the height is an influential factor.

The accuracy of these systems is highly dependent on the image processing software.

In the case of buildings, we believe this technology to be too sensitive and expensive compared to other solutions.

From our experience, no camera technology has yet attained the accuracy required in the transit industry. It is also the reason why we have not seen any installation of camera technology as a counting component in the transit industry. Camera technologies are suitable for surveillance purposes but not as a counting system in vehicles, since height is problematic at this point.

TREADLE MATS

Treadle mats are mounted in the step wells, replacing the existing treads on the steps. Treadle mats count by sensing the pressure of people’s feet as they traverse the bus steps upon boarding or alighting the bus or as they cross the entrance in the building.

Treadle mats usually serve one of three functions: To prevent the rear doors from closing on a person standing in the entrance or exit, to open the doors automatically and to be used as part of a people or passenger counting system.

Treadle mats are prone to damage from foot traffic, water and exposure to the elements. Moreover, these mats can be expensive to install, since proper fit and installation of the equipment is critical to the system's accuracy. Treadle mats also often need to be custom-engineered to fit the bus, with the switch elements placed for best counting accuracy.

Finally, treadle mats can be an acceptable solution for entrances equipped with steps, but they tend to loose their accuracy and reliability where the floor is level with the entrance.