Ultrasonic Motion Detectors

Hi,
i was wondering if anybody has done any installations using the Ultrasonic Motion Detectors (i think the cat no. is 752/225CU or something like that).

If i were to install a number of them into a large open area (say an open plan office), would the air movement from air conditioners tirgger the detectors?

If this was the case, how would you combat this, or does anybody know of any other Ultrasonics that are not easily affected by air movement.

thanks

 

Dual Detectors

All ultrasonic detectors can false trigger due to air-conditioning vents etc. and their placement near these vents should be avoided. (See manufacturers installtion and operating instructions). Clipsal also make a 752/225CUI (IR + Ultrasonic detector). This unit can be programmed to trigger if BOTH the IR and Ulrasonic sensors detect movement, this should help improvement detection reliability. Having said that, if you follow the guidelines set in the operating instructions regarding placement and sensitivity adjustment then you should be okay whatever sensor you use.

 

Stace.Is that really you ?

"if BOTH the IR and Ulrasonic sensors detect movement,"

Wouldn't this mean there would need to be more stimulus to trigger both sections of the detector as opposed to the "OR" situation ???

 

Missing in Action

Phil, yes it?s me, still alive but living in Malaysia.

In response to your query, the 752/225CUI can be programmed (by dip switches) to trigger if the IR sensor or Ultrasonic sensor or both sensors detect movement.

IR sensors respond to the movement of a thermal body, and IR sensors work best for large movements, such as someone walking, ultrasonic detectors set up a standing wave and when standing wave is disrupted, the sensor responds, the ultrasonic detector is best for fine movements such as someone sitting at their desk typing, like I am at the moment.

If you program the unit so that both sensors must detect movement, then you will minimize false triggering that may be caused from air-conditioning if this is a problem. If not ultrasonic sensors or IR sensors correctly placed will give you hassle free operation.

Generally, ultrasonic sensors are great for large open space areas, since you require less sensors to cover the same area as opposed to IR sensors, but in small offices (up to 6x6msq) I would use a good quality IR sensor, preferably a 360 degree sensor.

 

Ah but the problem is if you use a combined sensor it will only trigger on BOTH PIR and UltraSonic and so the effective sensitivity will be that of the PIR which often isn't enough to pick up me typing (or snoozing) at my desk.

I know that PIR's are range rated assuming a 90kg person walking at>1m/sec across the field of view with >5C temp difference to the background but what amount of movement triggers an ultrasonic and in particular what air flow (ie l/sec at ? distance) will trigger it.