N1 and EPR measurement.

[Elroy Jettson]

How is N1 and EPR measured on modern fans? Does anyone have a link to the electrickery behind it?:confused:

References to answers would be appreciated. :)

Thanks.

[VnV2178B]

Hi Elroy,

this will have to be a brief post just to give you a starter, I will try to sort out more later (work permitting!!)

N1 is easy - try looking for 'phonic-wheel' sensors : basically a winding on a magnet detects a cog wheel's teeth going past - same principle that a guitar pick-up uses. Electrically, the output is amplified, pulse-shaped and frequency detected to produce a signal output proportional to speed input.
Alternative methods sense the frequency of a dedicated alternator if there is a power take-off from that shaft this is usually not the N1 shaft though!

<edit>http://www.westonaero.com/products/how_speed_sensors.stm



EPR uses two pressures, the inlet duct pressure and the output jet exhaust pressure. These are sensed by using (in my case) 'oscillating cylinder' transducers. These are a cavity which is piped to the zone in which the pressure needs to be sensed with have an exciter winding and a sensor winding and vibrate a natural frequency which is pressure dependent. An amplifier keeps the oscillation going and a sensor and frequency to voltage converter produces the output. This needs to be compensated for temperature and other effects. Each transducer usually comes with its own calibration tables (dammit - if one breaks it makes life awkward reporgramming) - search manufacturers Solatron, Druck and Kulite.

VnV...