making a high speed tachometer

[abbaszandilak]

hi everyone. i want to make a tachometer with arduino mega. my main approach is using IR receiver and transmitter to capture the radial compressor blades' movement and I'm using BRQM100-DDTA sensor but I have some troubles like the sensor malfunctioning at high speeds.do you have any suggestions or idea about this?can I use the simple IR sensor and transmitters .i have to say that my compressor numinal speed is about 90K rpm.
thank you all
thank you edaboard

 

[betwixt]

If you are interrupting an IR light beam with the compressor blades, the frequency will be 90K * (number of blades) so it could be very fast. How many blades are there?

The response time of that sensor is quoted as <1mS which is only 1,000 interruptions per second. Far too slow!

If the blades are ferrous metal, it might be possible to use a reluctance sensor, otherwise a far faster optical sensor will be needed.

Brian.

 

[abbaszandilak]

If you are interrupting an IR light beam with the compressor blades, the frequency will be 90K * (number of blades) so it could be very fast. How many blades are there?

The response time of that sensor is quoted as <1mS which is only 1,000 interruptions per second. Far too slow!

If the blades are ferrous metal, it might be possible to use a reluctance sensor, otherwise a far faster optical sensor will be needed.

Brian.

thank you sir for your reply. the number of blades or 7 but I paint them 5 black and 2 silver to reflect the light.the reluctance sensor that you mentioned can operate at this speed?

 

[KlausST]

Hi,

what this compressor that runs with 90k RPM?
Where is a link to the datasheet(s)?
What does "malfunction" exactly mean?

the frequency will be 90K * (number of blades) so it could be very fast. How many blades are there?

Frequency usually is measured in 1/second where rotation is in 1/minute.

Klaus

 

[D.A.(Tony)Stewart]

BRQM100-DDTA specs:

Sensing type	Diffuse reflective type
Sensing distance	100mm
Sensing target	Opaque, Translucent material
Light source	Infrared LED(850nm)
Response time	Max. 1ms

1. Target distance : TBD , Closer is better for reflectance.
2. Target surface: 2 silver 5 black paint.
3. - Black may be reflective at 850 nm, common issue, degraded SNR,
4. - SNR may be improved with carbon type surface for IR
5. Target speed: 90k RPM = 1500 Hz, if 2 blades act as 1,
6. - Are 3 silver blades better?.
7. - if 1 ms response time = T , typically, fmax = 0.35 /T = 350 Hz . Cutoff or intermittent?)
8. Hysteresis: 20% at 100 mm
9. - What does target signal look like ? ( Do you have a scope? )
10. In order to create a Tach at f 1500 [Hz] 1 shot circuit must use pulse < 650 us
11. - What pulse width is used in tachometer ? Or is it a digital counter?