Hi all! Some time gao there was a bit of controversy as to what kind of motor EMT 927 and 930 have.
All the signs on the earth and the sky suggested induction motor while one of the reputable EMT servicemen (HM)
kept telling me it is synchronous.
Here is one example of such statements from some (official??) leaflet at the site of another reputable serviceman:
www.emt-profi.de/Dusch-pdf/emt930-e.pdf
and one more:
http://www.google.com/url?sa=t&rct=...sg=AFQjCNHp_7CP0yvrTzLmmCeJKOt5aezO0w&cad=rja
I've recently came accross these articles by Mark Kelly, which may give a hint:
http://www.clarisonus.com/blog/?p=92
http://www.clarisonus.com/blog/?p=96
I have not done the generator test he describes in Part I as I do not want to mess my alignment again,
but a couple of symptoms coincide, suggesting eddy current induction motor:
-pllying extra load by fingers slows the motor down
-big power: 30W 930 and IIRC 50W 927
Another symptom is the voltage-speed constant curve Kelly mentions in Part II. According to HM 930's motor "locks" (i.e. most probably he means "maintains a constant speed" if the motor is EC) at 90V. I have not checked that myself yet as my controller is still in statu nascendi.
On a related note here is an extract from VPI's SDS motor controller description:
"During motor startup, the SDS increases its output voltage in order to bring the platter up to speed quickly. Once the desired platter speed has been reached, the SDS ramps the output voltage down in order to reduce motor vibration and, therefore, the systems noise floor."
I'm wondering why lowering the voltage reduces the vibration? Although SDS is primarly for synch motors, Kelly's observation (provided EMT motors are EC) suggests one may try the same with EMT, reducing the voltage from 210V to approx. 90V.
Cheers,
phi