Trace Filterwheel Documentation The TRACE filterwheels are nearly exact copies of the MDI filterwheels. For top assembly drawings for the TRACE filterwheels are TRA-061003 & 004. The difference between the 2 filterwheel assemblies is the connector location. The drawing TRA-061052 shows how & in what positions the filters are installed in the wheels. There are 4 filterwheels available for TRACE, 2 left over from MDI & 2 purchased specifically for TRACE. The 4 filterwheels are identified as follows: 1) PAWFRM4 2) PAWFLM5 3) TRA-061003 4) TRA-061004 Differences between MDI & TRACE filterwheels: 1) Different connector location. 2) Code disk for TRACE wheels cover openings between filter locations. 3) Bearing lubricant for TRACE is Braycote 600 (MDI used Brayco 815Z). The drawing TRA-061052 shows the locations of the filters in both TRACE filterwheels. This drawing also shows how each filter is mounted into the wheels. There are 4 positions in each wheel. There are 3 filters (and one open position) in each wheel. The filterwheels use card selects 7 & 8 (see cs.doc). Specifications: Size: 4" square x 1" high (not including connector and cover fasteners). Mass: 380 grams (not including filters or filter mounting hardware). Operating temperature: 0 to 40 C. Operating voltage: 15 +/- .5 Volts, 5 Volts required for drive electronics. Operating current: 15 @ 90mA peak, 5 @ 80 mA. The following time measurements were made using TRA-061004 on 8-May-96. Time to move 90 degrees: 270 ms Time to move 180 degrees: 490 ms Time to move 270 degrees: 720 ms Time to reset: 366 ms Position repeatabilty: +/- 1/4 arc-min The motor will stop at a different position if it moves there in a clockwise direction than if it moves there in a CCW direction. For a particular motor voltage the wheel will stop in the same place in both directions. This voltage is 14.5 to 15 V for the TRACE motors. The sensitivity of the stopping position to motor voltage is about 8 arc-sec / V. Operation: The following commands can be sent: 0 Nothing 1 Move CW 2 Reset 3 Move CCW 4 Load Stopping Position 5 Read Encoder 6 Nothing 7 Nothing A CW move increases the encoder reading. The encoder counts 0 to 143. CW & CCW are wrong. When looking at the end of the motor where the filters go a CW command will cause the motor to turn CCW. That's just how it is. When power is first applied to the Filterwheel it must be reset before it is ready to be used. After a reset but before the first move command, the encoder reads 255. In normal operation the Filterwheel moves to one of 4 positions. The following tables show how to move from a position to any other. In general a different table may be required for each filterwheel. The tables arbitrarily show 2 CW and 2 CCW 180 degree moves. When the motor comes to a stop its position is nominally at an encoder transition, therefore a given motor position has 2 possible encoder readings. TRA-061003 (aft filterwheel) +------------------------------------------------------------+ | Present | Present | Desired Position | | Position | Encoder |---------------------------------------| | | Reading | 1 | 2 | 3 | 4 | |==========|=================================================| | 1 | 124/125 | - | 16,CW | 52,CW | 89,CCW | |----------+---------+---------+---------+---------+---------| | 2 | 16/17 | 125,CCW | - | 52,CW | 88,CW | |----------|---------+---------+---------+---------+---------| | 3 | 52/53 | 125,CCW | 17,CCW | - | 88,CW | |----------|---------+---------+---------+---------+---------| | 4 | 88/89 | 124,CW | 17,CCW | 53,CCW | - | +------------------------------------------------------------+ TRA-061004 (forward filterwheel) +------------------------------------------------------------+ | Present | Present | Desired Position | | Position | Encoder |---------------------------------------| | | Reading | 1 | 2 | 3 | 4 | |==========|=================================================| | 1 | 18/19 | - | 54,CW | 90,CW | 127,CCW | |----------+---------+---------+---------+---------+---------| | 2 | 54/55 | 19,CCW | - | 90,CW | 126,CW | |----------|---------+---------+---------+---------+---------| | 3 | 90/91 | 19,CCW | 55,CCW | - | 126,CW | |----------|---------+---------+---------+---------+---------| | 4 | 126/127 | 18,CW | 55,CCW | 91,CCW | - | +------------------------------------------------------------+ CONNECTOR: Pin # Function Backplane FW_1 FW_2 ------------------------------------ 1 Encoder RTN 24 34 2 Encoder A 25 35 3 Encoder B 26 36 4 Encoder C 27 37 5 IRED + 29 39 6 IRED - 28 38 7 Phase A 30 40 8 Phase C 32 42 9 Phase B 31 41 OPERATION BY THE CONTROL COMPUTER: The control computer (CC) automatically subtracts 1 from the set-position before sending that position to the filterwheel electronics if the next move is a CW move. That is done because the filterwheel always overshoots the set-position by 1 step when it moves CW.