HP 5501A Operating And Service Manual page 120

The 10755A Compensation lnterface Card recognizes two instructions, output and update.
Update comes from the coupler backplane, from the manual module's pushbutton, during
system reset, and after each output to the backplane.
When an update command occurs the interface card waits for the completion of the next
compensator computation cycle. It then presets four BCD down-counters with the 16 bits
from the compensator. At the same time it presets four binary up-counters with a 16-bit word
representing the least-significant 16 bits of the binary represenation of 9990000. The BCD
down-counters are then clocked down toward zero, and simultaneously the binary up-counters
are counted up. When the BCD counters reach zero, the binary counters hold a binary repre-
sentation of the lower 16 bits of a binary representation of the compensation factor.
Operation with the manual compensation module proceeds in similar fashion.
In addition to compensating for the variable speed of light, the use of the compensation factor
allows the operator to correct for thermal expansion of the part being measured or worked. All
dimensions are normally referenced to their values at 20.0°C (68.0°F); at higher temperatures
they measure longer or shorter than this, depending on whether the part has a positive or nega-
tive coefficient of thermal expansion. The 5510A Opt 010 Automatic Compensator has a special
thermal probe for sensing part temperature. The coefficient of thermal expansion i s entered on
the front of the unit through a set of thumbwheel switches. The compensator does the required
computation automatically and modifies the compensation factor accordingly. The same prin-
ciple can be applied when using the 10756A Manual Compensation module.
A special check mode of the automatic compensator causes it to output the measured values
of pressure, temperature, and humidity. These numbers can be placed on the backplane by
the compensation interface, and can be accessed by the system controller for setup or system
checkout. For additional information and schematics, refer to the 10755A Compensation
lnterface Operating and Service Manual.
Thumbwheel
1
I
W . ~ ~ m I a t i O "
Inverter Circuits
Switch
L
Figure 3-20. 10756A Manual Compensator