Fluke 45 user manual External Trigger, Update Rate in the Dual Display Mode

Applications 4

External Trigger

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.

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