Tektronix 485, Instruction Manual

Page: 58 / 197

Calibration—4 8 5 /R 4 8 5 Service
d. INTERACTION with 5 ns timing, repeat steps 26 and
27 if necessary.
31. ADJUST 1 ns T IM IN G
a. Set TIM E/D IV to 1 ns.
b. Adjust 1 ns (R1228), (located in back of the lower
relay on the Sweep board) for exactly 1 to 9 timing (four
2 ns markers over the center 8 divisions).
c. If exact timing cannot be achieved, a compromise
adjustment may be done.
32. CHECK 1, 2, and 5 ns SWEEP L IN E A R IT Y
a. Less than 0.1 division of error with timing adjusted
on (1 ns through 20 ns). With time marks exactly aligned at
1 and 9 the remaining marks must be no greater than
0.1 div away from their respective graticule lines. The
incremental error must not exceed 0.1 div over any one
division.
33. CHECK B SWEEP T IM IN G ACCURACY
a. Check timing over center 8 graticule divisions; posi­
tion one time mark to 1 and read error at 9.
b. 1 ns to 20 ns;—within 0.16 div (2%).
c. 50 ns to 0.1 s;—within 0.1 div (1.25%).
d. 0.2 s to 0.5 s;—within 0.16 div (2%).
34. CHECK A SWEEP T IM IN G ACCURACY
a. 1 ns to 20 ns;—within 0.16 div (2%).
b. 50 ns to 0.1 s;—within 0.1 div (1.25%).
c. 0.2 s to 0.5 s;—within 0.16 div (2%).
35. CHECK A U TO R E P E TITIO N RATE
a. Set A TIM E/DIV to 50
ms
; SWEEP MODE to AUTO
TRIG.
b. Check that sweep triggers on 50 ms markers and will
not trigger on 0.1 s markers.
36. CHECK D E LA Y T IM E A C C U R A C Y , 10 ns/
div to 0.5 s/div
a. Use time marks that give 1 to 5 markers/div on the A
display. Use B TIM E/D IV for 1 ns for A TIM E/D IV settings
of 10 ns through 0.1 Ms. For A TIM E/D IV setting of 0 .2
ms
and slower maintain an A:B ratio of 100:1.
b. Set the DTP dial exactly to the reference position
(1.0 except at the fastest speeds). Use the POSITION
(HORIZ) control to move the marker on the B display to a
reference position.
c. Rotate the DTP to 9.0 and then slightly from 9.0 to
place the B display marker to the same screen reference
position. Read the error (from 9.00) in the minor dial
divisions on the DTP dial.
TABLE 5-4
A Time/Div Reference
DTP
Position
Maximum DTP Dial Error at
Setting near 9.0 (minor
divisions)
10 ns 4.0 6
20 ns
2.0 7
50 ns to 1 ms 1.0 4
2 ms to 0.5 s 1.0 8
37. CHECK IN C R E M E N T A L D E L A Y ACCU­
RACY 10, 20, and 50 ns/div
NOTE
Check the erro r at each turn against the requirements
given in the chart a t the end o f this step. Detailed
procedure is given fo r the 10 ns/div.
a. A and B TIM E/D IV of 10ns and In s ; HORIZ
DISPLAY to B; A TRIGGER HOLDOFF to NORM; time
marks of 10 ns.
b. Set the DTP dial to exactly 4.0. Adjust the POSI­
TION (HORIZ) for marker leading edge at midscreen. Turn
the DTP dial CW one turn at a time and bring a marker to
the exact midscreen position.
c. Check that the dial errors at 5.0, 6.0, and 7.0 are
within the allowable limits (at 10 ns/div the change in error
over any one turn is not to exceed 2 minor dial divisions,
and the total error at any turn is not to exceed 3 minor dial
divisions).
5-14