Galvanic Applied Sciences ProTech903, Operation Manual

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Revision 14
22 August 02, 2019
2.6.2 Optical Encoder
The Optical Encoder is used to ensure even spacing of stains on the lead acetate tape. The
Optical Encoder is shown in Figure 2-5.
Figure 2-5: Optical Encoder
The left and centre pictures show the Optical Encoder as it appears when not installed in the
chassis and the right picture shows how the Optical Encoder appears in the tape transport
system. The black aluminum (or grey plastic) capstan is mounted on the silver nub seen in
the left picture, and it rotates when the tape moves over it.
The Optical Encoder produces a specific amount of pulses for every revolution. By measuring
the number of pulses produced by the movement of the tape while the motor is running, the
system processor can ensure that the tape is advanced exactly the same distance before
every analysis cycle, regardless of the quantity of tape on the take-up reel. This ensures that
the stain spacing on the tape is even; further, by reducing the amount of white space
between subsequent stains, tape wastage is minimized, and tape life is maximized.
When the motor advances the take-up reel, causing the tape to move, the movement of the
tape causes the capstan on the pulse-counter to rotate, producing pulses. These pulses are
read by the sensor block, which then sends the pulse count to the system processor. When
the processor receives a number of pulses equal to the number of pulses per advance set in
the application program; typically around 40 pulses, or a little less than one sixth of a
revolution, it sends a signal to the motor to stop turning, and the tape stops advancing.
The Optical Encoder also allows the system to accurately indicate the quantity of tape
remaining on the supply reel, as long as the initial length is set correctly in the application
program or through the keypad. This value is displayed on the LCD in the upper right corner,
and can be output through an analog output. The quantity of tape remaining is calculated
after every analysis cycle, using the formula outlined in Section 5.9.1.1. This value can also
be used to trigger a low-tape alarm when the quantity of tape goes below a user-set value,
set up through the application program.