What do I need to consider before installing the PIR sensor?
It is recommended to install the sensor at a height between 1.8m and 2.4m in order to get the best coverage of the area.
The sensor coverage area is approximately conical in shape and is broken up into zones by a Fresnel lense - see below for a view of coverage area. The target to be detected must pass either into or out of one of these zones in order to be detected. Small targets can sometimes move between these zones and not be detected because they never pass into or out of a zone.
Top View Diagram
Side View Diagram
Targets moving directly toward or away from the sensor may sometimes escape detection as PIR sensors tend to be less sensitive to this type of movement - this is most likely to occur with small targets.
Please note also that you should not point the PIR towards an area with constantly moving objects such as vehicles, small animals, hanging objects or trees that can move in the wind.
Unless necessary, for the best results, a target should move across the coverage area. Note how the zones are spaced wider near the end of the sensors range, and are shorter at the edges of the coverage area. At the far end of the detection area the sensor is covering the largest number of square feet. As you move closer to the sensor its coverage area decreases.
Temperatures can often change dramatically in relatively short times. Large temperature changes can render the PIR sensor either more, or less, sensitive. As ambient temperatures rise to near 37ºC, the difference between the target and ambient temperature decreases - and the sensitivity of the sensor declines. As temperatures decrease the opposite is true and the sensor becomes more sensitive.
As target and ambient temperatures become equal, the PIR sensor may no longer be able to detect a target. Large targets usually have enough variation in their surface temperature to allow the sensor to detect them - even when the ambient temperature is the same as their average body temperature.
The IN-Motion 500 PIR sensors compensate the PIR detector sensitivity according to the ambient temperature. But it is recommended to de-couple the microwave sensor from the PIR on hot summer days (or hot interior environments), to not solely depend on the heat detection! In the decoupled state (the DIP switch 5 needs to be in the OFF position) both sensors can trigger an alert.
How do I minimize false alarm by the PIR sensor?
The greatest drawback of the PIR sensor is that it will detect anything that is moving - hot air, cool shadows under passing clouds, rising heat stored in the surrounding vegetation, etc. - and has a temperature differing from ambient. The IN-Motion 500 has been optimized to minimize these problems, but in harsh environment settings, some false readouts are unavoidable. Below are some tips to help you minimize false events.
Direction Point the sensor away from the rising or setting sun. In general, North or South works well, but your local site conditions could dictate otherwise.
Warm Surfaces Keep the sensor aimed at an area that will not have intense, direct sunlight warming all or part of the detection area. Shadows of trees or clouds moving across a sun-warmed area can cause a momentary temperature drop which could cause a false event to be recorded. Warmed air rising from the ground can cause problems too.
Vegetation Tall, sun-warmed grasses or other vegetation blowing in a breeze can be detected. Point the sensor away from dense, sun-warmed vegetation which can trap heat.
Temperature Drops Even in a shaded area, keep the sensor pointed away from dense shrubs or trees that can retain the day's warmth. If the air temperature drops at night - and the still warm shrub moves in the wind, this movement could be detected.
Birds If the area is known to have many small birds / mammals, you will surely get many blanks, as these active, fast animals will often leave the frame before a picture can be taken.
Wind Wind can cause false events. The moving air might be warmer or cooler than the background. Place the sensor in an area sheltered from strong winds.
Installation Wind can also cause movement of the object you have your sensor mounted to. Make sure to secure your sensor to an object that will not sway in strong winds. Any movement of the equipment may be interpreted as motion by the sensor.
Target Size A small target near the end of the sensors range crosses only a tiny percentage of the total covered area and might escape detection. A small target close in to the sensor crosses a greater percentage of the covered area and is much easier to detect. A target's size, distance from sensor, and surface temperature play an important part in the sensors effective range.
How to Test?
Please conduct a walking test after installing the device onto a wall to ensure the device is functioning. Please check before the test:
- DIP1 & DIP5 switches are switched to “On”
- Ensure all wiring is correct
Step 1. When power is on, please wait for 15min for the device has finished self-inspection (red LED will stop flashing once done) and for the sensors to warm up. When moving within the detection area, the red LED will light up and signal a detection if both sensors detected you. After 2s of no movement, the LED will turn off. Wait for 15s for the sensors to become active again.
Step 2. Now walk to edge of the detecting area, check the LED status. The blue LED will be on if you are within the PIR detecting area and it will flash if you are in the microwave detection area.
Step 3. Repeat step 2 on all edges of the detection area to see if it covers your required area. The red LED has to light up in order to signal you that both the PIR and Microwave sensor detected you.
Step 4. You may adjust the Microwave strength clockwise to strengthen the sensitivity - if required.