Reduce PIR Sensor Sensitivity?

I have a robot on which I wanted to add a PIR sensor to be able to detect when a human (or anything living really) crossed in front of it. The robot then apologizes via LCD screen and takes another path. However since the addition of the sensor, it is tripped by just about everything, even the robot moving forward slightly with no people or significant heat sources near it. My understanding of these sensors is that they measure average IR radiation and so I imagine the problem is that even though there are no high IR radiation sources changing the average IR, the movement of the robot is still changing the average IR radiation of the environment the sensor is measuring. So long story short, is there a method in which I can make the sensor less sensitive to these low level IR sources? If I could get the sensor to only measure high radiation sources that would be ideal, otherwise I'll have to purpose the sensor into something stationary I guess.

Thanks for your time and help

Sensor is a HC-SR50 purchased from:

Those are complete sensors to detect motion. You can't adjust them for your need.

Suppose the sunlight is entering a room, and the robot is moving. The PIR 'sees' the difference between the places with sunlight on it and the other parts. So the sensor 'thinks' it sees something hot moving, and detects it.
With a sensitive sensor, it will result in what you described.

You can use tape to disable a part of the sensor angle. For example less up and down.
I think you have to stop the robot to be able to detect motion.

PIR establishes a snapshot of the environment while it settles. Then it alarms if the environment changes from that snapshot. So, if the robot is stationary and takes its snapshot, then moves, the environment changes compared to what it saw a second ago, and it alarms.

PIR's not the right sensor for that application.

Thermal imaging sensors do respond to the average IR field, detect IR sources and can be used to track humans. Melexis makes thermal imaging chips with single pixels and also arrays ranging from 2 to 8 pixels or 16x4, that can form images of the IR field. See the later posts in this thread for some suggestions: http://forum.arduino.cc/index.php?topic=199482.0

Melexis chips are described here: http://www.melexis.com/Infrared-Thermometer-Sensors/Infrared-Thermometer-Sensors/MLX90614-615.aspx

try an ultrasonic sensor instead...

Thank you for all your input, I will have to rethink the objectives of the robot. I will certainly look into those thermal imaging sensors jremington. AnalysIR, the robot already has three ultrasonic sensors for obstacle avoidance, the goal was to differentiate between humans and the rest of the environment and respond appropriately.

Thank you again