Strobe light?

[Agile]

I need to be able to measure/check the speed of boiler fans.

Has anyone used a strobe light of any kind for this purpose?

Might be called optical tachometer or ( wrongly ) stroboscope.

This would seem very useful:-

http://www.gyroscopes.co.uk/d.asp?product=TACHOMETER2

Tony

 

[breezer]

Has anyone used a strobe light of any kind for this purpose?

car mechanics.

FACT: a flourescent tube has the same effect, which is why you should be carefull installing them above spinning machines, (but there are ways round it)

 

[Agile]

The old timing light was used for a slightly different purpose, to illuminate a timing mark on the flywheel at the moment the contacts opened.

Boiler engineers need to be able to measure the actual speed of the fan which required a calibrated strobe light.

Does anybody know the typical speed of a shaded pole fan motor in a boiler?

Tony

 

[TicklyT]

We used to use a 'stroboscope' for checking motor speeds. It was just a tuning fork with a pair of slotted shutter blades on the tips of the prongs. Strike the fork, and look through the shutter at a white spot painted on the rotor, and see which direction it appeared to spin (ideally it appeared stationary). The DC motors in this application were very tightly governed as they provided a signal timing source. I don't know if such a simple 'mechanical' device could be used where tolerances are wider.

 

[heatingman]

Why do you need to know the speed at which the fan is spinning?

 

[Agile]

If a boiler fan is not turning at the correct speed then the combustion characteristics will not be correct!

Tony

 

[freeflow]

is it just one boiler in particular that you need to test? i know with the greenstar's, they spec an upper and low limit measurement in hertz in one of thier service guides.
or another way to test the fan force ( maybe? ) would be to use a anemometer on the flue outlet duct.

 

[holty]

agile is it zero governors your on about as i thought the fan speeds were checked by the pcb by the hertz the fan produces.

 

[Softus]

Boiler engineers need to be able to measure the actual speed of the fan which required a calibrated strobe light.

You're making it up as you go along.

If you're going to measure fan speed and do anything useful with the information, then you'll also need to measure precise fan blade angle, effective flue length, height of the terminal above sea level, and phase of the moon.

 

[gas4you]

 

[heatingman]

I find a fga & readings do the job for me.

 

[grahamderek]

Quote, "You're making it up as you go along"
Situation normal then.

 

[Softus]

To be fair to Agile, he's an extremely knowledgable and competent boiler engineer.

 

[Agile]

I was posting about conventional shaded pole induction motors as used in all boilers before the advent of pre-mix.

Premix either drive the fan in a stepper motor mode or have a DC fan and feedback the actual speed from a Hall effect sensor. Most of the latter enable the actual fan speed to be read within the diagnostics.

Its not strictly necessary to know the exact fan speed but it is important to know that its correct.

An anemometer in the flue exit would also give a useful indication but the fan speed will probably be more relevant.

Tony

 

[Softus]

Oh JHC I've created a monster.