Fluke 45 - Manual (Page 54)

Applications
External Trigger
4
4-7
Update Rate in the Dual Display Mode
The update rate is the time between successive measurements for a steady state signal.
In the dual display mode (when both the primary and secondary displays are on), if the
measurement functions or the ranges selected for the primary and secondary displays are
different, the update rate for each measurement function will vary from the update rate
for that measurement function when only the primary display is on.
When the secondary display is on, the meter always waits for the measurement to be fully
settled after changing the range or function before displaying a reading. The amount of
delay depends on the functions and ranges selected for the primary and secondary
displays as shown in Table 4-3.
AC and DC voltage measurements, however, are always optimized to be measured with a
minimum of delay (including ac + dc volts). For these measurements, the update rate is
the update rate for each single display measurement plus an additional 75 ms.
Table 4-4 lists the interval between measurements when the measurement function or
range of the primary and secondary display differ. These intervals vary by measurement
function, range, measurement rate (slow, medium, or fast), and measurement type (ac-and
dc-type measurements mixed or not mixed).
External Trigger
The external trigger can be used with or without settling delays, as shown in Table 4-3.
(Refer to Table 5-3 for trigger types.) The amount of trigger delay varies depending on
differences between the primary and secondary displays, as described in the previous
section.
When external trigger is enabled, the meter determines the ranges for the primary and
secondary (if enabled) displays based on the input at that time. The meter is then ready to
begin measuring the input on the optimum range as soon as the trigger is received. If the
input changes so that either display autoranges after the trigger is received, the autorang-
ing response times (as shown in Table 4-2) may be required before each measurement
result is displayed.
The rear panel trigger input is level sensitive. A high level (above +3 V) will be
recognized as a trigger within at most 3 ms (more than 3 ms if the computer interface or
front panel is being used during the trigger time). If the trigger input line is still low when
the previously triggered measurement is completed, another measurement will be
triggered.