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P O L Y T E C H . N U
English

Collins CSS-10 synchro source

English introduction
This article is about the Collins CSS-10 sunchro source. This device is a housing containing two resolvers, one synchro transformer and two synchro transmitters.

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English use
This synchro source is intended to use as a test device for avionics. This device can generate two sets of sine/cosine resolver signals to control an avionics device. A avionics instrument that is controlled by a resolver signal, can be tested/verified using this signal source.

Each control is equipped with a dual control knob. The inner knob is connected directly to the resolver/synchro. One rotation is 360 degrees and the scale markings are per ten degrees. There's also a ring around the inner knob that's used for precision control. Each rotation is 20 degrees and the scale markings are per 0,2 degrees. This makes is possible to control the settings with rather high precision.

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This signal source device can act as a substitute for a gyroscope for example. I connected the synchro transmitters to the pitch and roll input of the Smiths H6 director horizon to simulate the movement of a gyroscope. The two resolver outputs are also used to control the glideslope indicators of the director horizon. So the director horizon can be tested without a gyroscope.
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A first test video of the setup is shown below. Note that the setup reacts rather slow. This is due to a too low synchro voltage in this setup. In normal operation the speed is much higher.



In the older test video using a loose synchro the speed is much higher as you can see below. The speed is now good since the right voltages are used.


English description
The synchro source is a device that can create signals for avionics testing. Each control is used to determine the angle of rotation. There are five controls and three different kind if controls:

resolver 1 and 2 (two left controls)
The resolvers have to be fed with a 26 VAC 400 Hz reference signal. The rotor in the resolver created therefore a 400 Hz magnetic field. There are two other (fixed) coils namely the sine and cosine coil. Both wires of each coil are available as the signal output. Depending on the mechanical rotation (by the knob) of the rotor, the signal amplitude and phase changes. Analog Devices made a nice graphical representation of the working shown below. (Thanks to http://www.analog.com.)

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synchro transmitter 1 and 2 (two right controls)
The working of the two most right controls are almost identical to the resolver. There's a 28 VAC 400 Hz signal needed to the rotator reference winding to induce a magnetic field. Instead of two independent (90 degrees separated) windings in a resolver the synchro has three linked windings. Each output line has a 120 degrees shifted phase. So when rotating the synchro transmitter knob, the rotor winding is rotated resulting in changing of the amplitude and phase of the output wires.

synchro transformer (middle control)
The synchro transformer is a little bit different than a synchro transmitter. Where the synchro transmitter has it's input at the two wire rotor and the three wires are used as the output, the synchro transformer works reversed. The three stator wires are the input and the two rotor wires are the output. When a three wire synchro (transmitter) signal is applied to the three wires of the synchro transformer, a signal is induced at the two wire rotor output. When the phase of the reference signal input of the synchro transmitter is aligned with the output of the synchro transformer, the angle of both synchro's are aligned. The difference in signal is proportional to the angle change between the synchro's. Thus a synchro transformer can be used to verify the angle of the synchro transmitter by rotating the knob and reviewing the synchro transformer output signal.

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English schematic and connections
As can be seen on the schematic, the device is rather simple. Altough it's rather simple, the precision of the device stands out. There are two resolvers, one synchro transformer and two synchro transmitters built into the device. Each wire of these five instrument are linked to a test point at the front panel. All the wires are also connected to circulator connector J100 at the rear panel. The synchro's wires are also connected to connector J101. Remind that for the two synchro transmitters the common rotor wire is connected to one pin 'F'. Connector J101 has 'only' 14 pins and 15 independent pins are needed for the three synchro's. Since the synchro transmitter rotor wires are usually tied together, the common pins is already connected together to fit all the wires to the 14 pin connector. Each device is designed for 28 VDC 400 Hz.

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English inside view
The inside of the device is rather boring. There are just five resolvers/synchro's with the dual speed drive, two connectors and some wiring. The device is well designed and well built. Wires are tied together nicely and it's built to last... Each of the five instruments are calibrated by rotating the resolver/synchro mechanically. Each device is fitted with three screws. By loosening the screws a little bit the device can be rotated to the desired position.

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English purchase
On october 2023 I visited a Dutch ham fest in the city of Zwolle. When I arrived at the market my eye was caught by this instrument. I read 'resolver' and 'synchro' on the front panel and knew this could be interesting for me. The device was well prices and therefore I made my first purchase of the day in the first minute visiting... The knob of the second resolver was stuck since the axel was bent, but this seems repairable. Based on the label the device was used by KLM; the Dutch royal airline company. During inspection I discovered that the most right synchro was loose and the coupling was a little bit bent. The damage was probably the cause for taking the device out of service. Since the device has a rather specific use, the device travelled probably from one to another ham fest for a while before selling. You may imagine that this find is the find of the century for me. This type of devices are rather rare to find for a hobbyist like me.

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repair