HP 5501A Operating And Service Manual page 114

NOTE
See 107648 manual for differences between 10764A and 107648
cards. Power supply requirements, jumpers/switches, and oper-
ating temperatures are different.
3.18
10764B Fast Pulse Converter
The 107648 Fast Pulse Converter is used in a comparator-based computer interface system in con-
junction with a comparator card to increase the measurement resolution and velocity of the Laser
Transducer System. Refer to Table 3-3 typical comparator-based computer interface specifica-
tions for allowable resolution and maximum velocity specifications for specific interferometers.
The fast pulse converter (Figure 3-75) provides a means of converting the reference and measure-
ment signals from two axes to pulses that can be counted by the comparator card. The reference
and measurement signals are applied to signal reception and isolation circuits.These circuits con-
tain photo-isolation devices which convert the differential input signal pairs to single-ended
signals with ECL logic levels. Additional immunity to external noise i s obtained by applying these
signals to Schmitt trigger circuits.
The resolution selection circuits allows resolution extension of the system by factorsof 1 through
15. The pulse generation circuits compare the input signals (derived from the incoming reference
and measurement signals) with respect to frequency and outputs a pulse for each 1/2 cycle dif-
ference between the reference and measurement signals. If the reference signal frequency is
higher, pulses occur on the down-pulse line; if the measurement signal frequency i s higher,
pulses occur on the up-pulse line.
Error detect circuits monitor the incoming reference and measurement signals for extreme fre-
quency. If the frequency deviates from its nominal value by greater than preset limits, an error
signal is generated. The only instructions that the fast pulse converter responds to are reset error
bits and output error bits.
For additional information and schematics, refer to the 107468 Fast Pulse Converter Operating
and Service Manual.
Input
Isolation
i
Circuits
I
P I (Coupler Backplane)
(From Head) Ref
(From Axis
1) M1
(From Axis 2) M2
P I (Coupler Backplane)
Rerolrttion
i
Switch
Selectal~le
I
90 MHI
Clock
Figure
3-75. 70764A
Fast
Pulse
Converter Block
Diagram