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WB4GQK > INFO 06.07.02 14:05l 49 Lines 2758 Bytes #999 (0) @ WW
BID : 22708-W4DPH
Read: DB0FHN GUEST
Subj: Re: SELSYNS
Path: DB0FHN<DB0ZWI<DB0CHZ<OK0PKL<DB0MRW<OK0PPL<RZ6HXA<IK1ZNW<HA3PG<JE7YGF<
XE1FH<W4DPH<W4DPH
Sent: 020706/1148Z @:W4DPH.#TPA.FL.USA.NA #:22708 [CLW] FBB7.00g $:22708-W4DPH
From: WB4GQK@W4DPH.#TPA.FL.USA.NA
To : INFO@WW
Hi Warren and all,
Well I worked with SELSYNS and SYNCHRO systems in the Aerospace industry for
many years. All of my experience was with 400 cycle systems. So some small
corrections may be necessary when working with 60 cycle units. Specifically in the area
of "Static Accuracy". The limiting factor is related to phase shift of the applied
frequency, and this is what determines the "Position Error".
To begin with there are three (3) methods of sensing and controlling Selsyn positions.
#1 (we used to call brute force)was to use 2 Selsyns. One was the "GENERATOR" or
also referred to as the "CONTROLLER". The other unit was called the "REPEATER".
The fields were 3 phase and wired directly to each other. An external 3 phase 400 cycle
supply fed the fields. The rotors were single phase windings and also connected
together. When the controller rotor shaft was turned the repeater rotor would follow the
position with some lag depending upon the load on the shaft and the phase shift
comparing capability of the field and rotor windings. The voltage generated by the
control unit being applied to the repeater coil winding caused the reaction force that
turned the rotor.
#2 method was called the "voltage source" method. In this setup only one Selsyn was
employed. The field was supplied with the 3 phase 400 cycle source. The rotor coil was
supplied from two of the 3 phase voltage source wires. A potentiometer between the 2
phases would adjust magnitude and phase shift applied to the rotor. The rotor would
turn until the 3 phase induced voltage in the rotor matched the voltage and phase of the
output from the potentiometer. This was a null type system and only used with rotation
angles up to 120 degrees primarily fins or control surfaces. It was possible to obtain
some reasonable rotational force, of course not as powerful as hydraulics.
#3 method was called the "Potentiometer System". It also used only one Selsyn. Two
potentiometers were used and were tied across 2 of the 3 phase supply lines. 1
potentiometer was attached to the shaft of the Selsyn and it's center tap along with the
center tap of the controller potentiometer fed the rotor winding. As the rotor turned and
rotated the pot, it physically matched the electrical value of the control pot which nulled
the voltage supplied to the rotor winding. This type of system generally had 2 sometimes
3 step voltages that would greatly increase the position accuracy. Sorta like a "coarse-
fine-extra fine" accuracy.
You know after being pulsed like this it makes me want to get off my duff and pull out
some old papers stuffed in a box in the attic, maybe just for the fun of reliving old times.
THANKS!
de Jim wb4gqk
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