Specifications

Guide to Operation - Menus
30
GATE MENUS
The A GATE and B GATE are identical in
operation. The discussion below describes the A
GATE menu. The B GATE menu is similar, the
only difference being that A GATE enables A
counter and B GATE enables B counter.
In order to provide 1 part in 1000 settability, gate
delay, width, and scan step times have variable
resolution depending upon the 4 most significant
digits of the time.
4 most significant digits
resolution in 4th digit
1000 to 2048 1 (1001, 1002, 1003, ...)
2048 to 4096 2 (2048, 2050, 2052, ...)
4096 to 8192 4 (4096, 4100, 4104, ...)
8192 to 9992 8 (8192, 8200, 8208, ...)
Below 1.000 µs, the resolution is 1 ns.
For example, near 10.00 µs, the allowed times are
9.984 µs, 9.992 µs, 10.00 µs, 10.01 µs, etc. In each
case, the resolution is 1 part in 1000 or better.
Note that gates may be missed or truncated while
gate delays or widths are changed. Changing gate
parameters while counting may therefore cause
bad data to be collected. While scanning, all
changes to the gate delay are made during the
dwell time and do not affect the count data. The
GATE outputs may show missed gates during the
dwell time.
A GATE= CW
FIXED
SCAN ∆=1.000 µs
The A gate enables the A counter in three modes.
CW is continuous gating; counter A is enabled
during the entire count period. FIXED delay and
width enables the counter only during those gates
which occur during the count period. SCANning
increments the gate delay between count periods
during a scan.
The gate may be viewed through the A GATE
output. The counter is enabled when the output is
NIM low. If the mode is CW, the output is always
low, otherwise, it is low only during the gate.
If the gate delay is scanned, then the right hand
parameter is the step size. At the end of each count
period in a scan, the delay is incremented by one
step size. The step size can be varied from 0 to
99.92 ms. The range of a scan is N PERIODS
times the step size. The starting value of the delay
is set in the next menu line.
The scan mode may be changed during a scan. If it
is changed to SCAN, the delay begins scanning
from the start position on the next count period. If
it is changed to FIXED, the delay returns to the
start position immediately.
The step size may also be changed during a scan.
The new step size will be in effect at the end of the
next count period. The scan is not reset or paused.
A DELAY =****
=1.000 µs
: 2.000 µs
This line is inactive if the A GATE is CW. Even
when this is the case, the RATE LED will flash if
the trigger frequency exceeds 1 MHz.
If the A GATE mode is FIXED or SCAN, then the
delay of A GATE from trigger may be adjusted
from 0 to 999.2 ms. This is in addition to the fixed
25 ns insertion delay. This delay is the fixed delay
when A GATE is FIXED and the starting delay
when A GATE is SCANned.
The delay can be as long as the time between
triggers minus 1 µs. This is independent of the
gate width. Delays longer than the trigger period
minus 1 µs will result in missed gates and the
RATE led will flash.
When the A GATE mode is SCAN and a scan is in
progress, this line displays the current position of
the A GATE delay. The cursor is inactive and
replaced by a ':'. The spin knob cannot adjust the
delay while it is scanning. When the mode is
SCAN, the starting delay may only be adjusted
when the counters are in reset.
Because of the variable resolution of the delay, the
scan step may be less than the resolution of the
current delay. In this case, the delay is
incremented every n count periods where n is the