Protective shield for IR temp sensor
Brian Smith
Posts: 44
I was wondering if placing a clear plastic lexan shield infront of an IR temp sensor (such as the Melexis MX90601 style sensor)·would mess up my temperature readings. I could use clear tape if this would work better. I need to protect the sensor from small flying rocks/road debris. The sensor is encased inside a steel tube except for the exposed lense.
Comments
How about some small screening with the IR laser shooting thru a large enough hole. It will protect against 'MOST' debris....but like anything, it's not totally protected (some black boxes are unrecoverable too!)
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I agree with Steve. Lexan is treated to reflect harmful UV rays, this is bound to have an effect on IR emissions. I have seen sumo bots with their frames constructed out of Lexan. On each of every example I've seen, the IR detectors are either peeking out of an exposed slot, or are mounted outside of the frame. I'd try Steve's idea or maybe instead of screening, you might want to look at using an optical filter that will allow IR emissions.
Regards,
Michael G. Jessat
For this product I would first drill a hole the diameter of the sensor window, then drill the same hole with a bit that is the outer diameter of the sensor to a depth equal to the height of the sensor and mount it inside.
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
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The Melexis MX90601 is designed to detect infrared photons with a wavelength of 7.5 to 13.5 microns(long wave IR).
Photons in this band are absorbed by glass so you cannot use a glass window to protect your sensor.
However, a number of plastics such as polyethylene and the acrylates(Lucite, Plexiglas) are fairly transparent
to long wave IR and you could try these.
I would suggest setting up your sensor and placing various materials in front of it to see how much the signal
from a warm emitter(like your hand) is attenuated. You might try the following materials:
1. A clear plastic freezer bag.
2. The bottom of a plastic cup.
3. Thin Lucite, 1/8" max.
4. Thin Lexan
5. A thin piece of silicon (the kind that ICs are made of)
6. A piece of window glass (this should block the signal)
Dave G
I could also use some help getting the code right to read this sensor. I plan on using the digital output mlx90601-daa and im not exactly sure how to read the duty cycle or error mesages for that matter.
' {$STAMP BS2}
' {$PBASIC 2.5}
timeCounter······· VAR· Word·············· 'Declare variable to store time.
DO··············································· ·'begins main loop
··· timeCounter = 0························· · 'Set timeCounter to zero.
·PAUSE 13
··················································· ·'omits t1 from dutycycle calc
·DO
·· timeCounter = timeCounter + 1
·LOOP UNTIL IN3 = 0
· DO
··· DEBUG "temp is ", DEC (timeCounter),
········· " deg.", CR,CR
········· DEBUG HOME
· LOOP UNTIL IN3 = 1
LOOP
this is a very basic start and it wouldnt give the propper temperature output or tell me about errors..·Is there a better way? Melexis says that the value for T can varry and will not always be 102.4 ms. What do I need to do about that?
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Jon Williams
Applications Engineer, Parallax
Post Edited (Brian Smith) : 6/27/2005 8:27:00 PM GMT
Which version of the MLX90601 do you have? It states that several versions exist. Looks like some have analog output, PWM output or an SPI interface. That might point us in the right direction.
Regards,
Michael G. Jessat
its the MLX90601EZA-DAA with PWM output
So what is time controll and how can I use it?
I havent tried any dikfferent shielding for the lens yet.
The MX90601 uses a thermopile detector, which has a very slow response time, 1/2 sec. When you do any
calibration, you should let it stare at the target for at least 2.5 seconds(5 time constants) before reading the output.
Dave G