Need Advice on SENSORS for a project

[Megahertz]

I need advice on choosing two sensors for an industrial project involving cranes. I would like to ask if someone has any experience in this field and can advise me of some suitable sensors for the following:
1) Need one sensor to measure the distance in straight-line-of-sight of upto 10 meters maximum. I have been looking at some options involving laser distance modules but could not find any suitable options.
2) Need one tilt sensor to measure the angle, one axis measurement will be fine.

Thanks

[HenrikOlsson]

Hi,
You're not saying what type of accuracy or repeatabillity you want. 10m is quite a bit if you're looking at 0.001mm resolution, not so much with 1mm resolution etc. Perhaps a draw wire potentiometer (http://www.unimeasure.com) is an option (other names for the same thing exists). Or you might want to have a wheel riding along same the surface as the crane, this wheel is coupled to a 10 or 20 turn pot. Or you can use an absoulte (or perhaps even an incremental) encoder incorporated in the cranes existing wheels, or.....

For the tilt angle it again depends on the accuarcy and resolution and (but certainly not least) the mechancis to which it's going to be mounted. Perhaps a simple pot might do, or perhaps some sort of encoder ((incremental or absolute) optical, magnetic, capacitive etc), or perhaps an acceleromter will do?

/Henrik.

[Megahertz]

Hi,
For the tilt angle it again depends on the accuarcy and resolution and (but certainly not least) the mechancis to which it's going to be mounted. Perhaps a simple pot might do, or perhaps some sort of encoder ((incremental or absolute) optical, magnetic, capacitive etc), or perhaps an acceleromter will do?


I found this IC - http://www.muratamems.fi/sites/default/files/documents/sca61t_inclinometer_datasheet_8261900a.pdf
sca61tfa1hig - part number which can measure 0-90 degrees.

On page 3, section 1.2, under performance characteristics I can see it says measurement in "+-1 g". I would like to ask:

1) This seems to be measure of acceleration, but I do not see any separate output for measured acceleration on the IC.
2) If I just want to measure the angle lets say after every 250mS or 500mS, - Is this sensor suitable OR measurement of acceleration will be integral to the calculations involved.
3) If acceleration is involved then if lets say the object is stationary at 30 degrees, will this sensor output 0?

Also I read that the sensitivity is 2V/G - Please could you clarify what it means? Thanks

[HenrikOlsson]

Hi,
1) Yes, the sensor measures acceleration and that's what it outputs. The analog output "rests" at Vdd/2 and then outputs a voltage of 2V/G (that's sensitivity you askes about). So if Vdd is 5V you'll get 2.5V at 0G, 0.5V at -1G and 4.5V at +1G, for the +/-90° model. Likewise the SPI output specifies a digital offset of 1024 and a sensitivity of 819LSB/G. So at 0G you'll get 1024, at -1G you'll get 205 and so on.

2) Yes, it suitable but you need to convert the raw acceleration values to real incline/angle (it's not linear). See formula under section 2.5. But remember, it measures acceleration, so if any accelrations other than the earths gravity acts on the sensor you'll see that in the sensor output.

3) Yes, if the sensor is stationary at 30° it will output the raw acceleration value (caused by the earths gravity acting on the sensing element) for that angle. A gyro on the other hand would not output anything.

If this is for balancing something that moves "just" measuring the angle is what's hard.

/Henrik.

[ScaleRobotics]

That's an interesting sensor. It has a ratiometric output. See section 2.2 for straight line equation. But this seems to get high errors above 30 degrees (I think maybe that's why they dont list higher values). For more accuracy, they recommend the arcsine equation.

The http://www.sparkfun.com/products/8656 is the only sensor I know of that outputs in degrees, and its very pricey.

Here are a couple ways to get tilt:
Lookup table example: http://www.picbasic.co.uk/forum/showthread.php?t=16609
atan2 example: http://www.picbasic.co.uk/forum/content.php?r=210-Angle-determine-tilt-from-3-axis-g-sensor (sorry, its not documented very well)