Protek 9216A, Руководство пользователя, Страница: 28 / 77

27
Autoranging Mode
During normal operations, the meter automatically changes to the most accurate
range for the device under test. When the meter measures an impedance that is
out of its current range, it goes up or down one range, and makes another
measurement. If this measurement is within the current range, it displays it. If not,
it changes ranges (if available), and repeats this process. There is built-in
hysteresis to avoid repeated range changes when a component is on a range
boundary. Up-range changes occur when the impedance measured exceeds
450% of the mid-scale impedance (i.e, the source impedance), or 12.5% over the
nominal range limit. Down-range changes occur when the measured impedance
drops below 22% of the mid-scale impedance, or 12.5% below the nominal range.
See Table 3-5 for the actual values where the range changes occur.
Table 3-5 Range Change Points When Autoranging
Ranging To Lower Impedances Ranging To Higher Impedances
Range Change Impedance Range Change Impedance
2 to 3 Z < 88

3 to 2 Z > 115

1 to 2 Z < 1.4 k

2 to 1 Z > 1.8 k

0 to 1 Z < 22.4 k

1 to 0 Z > 29.9 k

RANGE HOLD Mode
It is sometimes desirable to disable auto ranging since it takes nearly a complete
measurement cycle each time a range changes occurs. This can be annoying if
there are no parts in the fixture and the meter is continuously triggering, since an
empty fixture appears as a very large (nearly infinite) impedance. The meter will
auto range to range 0 (range 1 for 100 kHz) and then auto range back to the
appropriate range when a part is inserted in the fixture. Range holding is helpful if
measurement speed is a concern or if a number of parts with similar values are
being measured.
There are two ways to implement a RANGE HOLD mode:
1. The present measurement range can be held simply by pressing the
HOLD key. The LED above the HOLD key indicates that the meter is in the
RANGE HOLD mode.
2. A measurement range can also be directly entered from the ENTRY
display. Select the ENTRY display using the
DISP key, then press HOLD .
The message “range” will appear in the left display, and the present range, 0–
3, will appear in the right display. Enter the desired range and press the
ENTER button.
Use the DISP key to return to the desired display. The RANGE HOLD LED will
be on. If an invalid range is entered, the meter will beep and display the message
“range error” and not accept the range entry. Range 0 cannot be entered when
the frequency is set to 100kHz. If this is attempted, the meter will beep and
display an “r-f error” (range-frequency error). To return the meter to the auto
ranging mode, simply press the
HOLD button.