VTI Instruments Ametek EX1200A Series, User Manual

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VTI Instruments Corp.
82 EX1200A Triggering
For example, if a 9 V signal is fed to the DMM and auto-range is enabled, the 10 V range is
selected in order to display 9.00000 V (the total number of digits is based on the resolution
selected). If a 1.12 V signal is fed to the DMM, the 1 V range is selected rather than the 10 V
range, as the input is within 120% of the range value. If, however, 1.3 V is fed to the DMM, the
10 V range would be used. Refer to Table 4-2 for valid ranges the auto range mode can select.
The auto-range mode is useful when the incoming signal voltage range is unknown or when it
varies largely over time. However, auto-range requires more time to complete the measurement
(slower scan rates) due to increased internal processes than if a manual range is selected.
Auto Range OFF and Auto Range Once
In Auto Range OFF mode, the last selected range, whether it was selected automatically or
manually, is used. This feature can be used to turn off measurement auto-ranging and fix the range
to its last know best fit.
When Auto Range Once is used, auto-ranging is performed for the first measurement only and
automatically disabled for further readings/scans.
NOTES For temperature measurements, the DMM internally determines and selects the range. This means
that range cannot be selected for temperature measurements. For thermocouple measurements, the
instrument internally selects the 100 mV range. For thermistor and RTD measurements, the DMM
auto-ranges to the correct range for the transducer resistance measurement.
If a positive, real number is passed in the API that is not one of the valid ranges for the selected
function, it will be coerced to next highest range available.
Range Delay
When the range of a function is changed, the DMM requires time to settle to the new range. The
“range change delay” is the amount of time the DMM takes to settle between measurements for
the same function on different ranges when in auto-range mode. This affects the speed of the
scanning operation. It is advised to group the channels in such a way that the number of range
changes are minimum in a given scan cycle. The range delay is the inverse (1/x) of the range
change event specification on page
Error! Bookmark not defined. .
Function Range Change Event Range Delay
DCV and DCI
300/s 3.33 x 10
-3
s
4-wire resistance (100
Ω
, 1 k
Ω
) 300/s 3.33 x 10
-3
s
2-wire resistance (<1 M
Ω
) 2/s 0.5 s
ACV (0.1 V to 100 V, high filter) 1.25/s 0.8 s
ACI (0.01 A & 0.1 A, high filter)
< 0.2/s 5 s
T
ABLE
4-3: R
ANGE
D
ELAY
R
ESOLUTION
To further optimize the speed and accuracy of DMM measurements, the resolution of the
measurement reading can be adjusted for most functions. Resolution is expressed in terms of
number of significant digits the multimeter can measure: 3½, 4½, 5½, or 6½-digits. The DMM
determines the aperture time based on the following algorithm: