8588A/8558A
Operators Manual
76
Note
In the Ohms function the scan operation switches both current
stimulus and potential difference measurement between the front
and rear terminals. This operation, also called Tru Ohms Ratio,
scans only the potential difference measurement between front and
rear terminals, maintaining the common stimulus current through
front and rear terminals. See 4W Tru Ohms Scan Mode (Tru Ohms
Ratio).
Scan Sequences
As the Product scans, each trigger event produces one scan result. The trigger
settings determine all the readings that make up a scan result. Scan runs through
this sequence for all scan operations except Tru Ohms Ratio, described below:
1. The Product waits with the rear terminals selected, and with the front
terminals isolated.
2. Upon receipt of a trigger, the Product executes any trigger delay.
3. After this delay, the Product changes to select the front terminals with the
rear terminals isolated.
4. The Product executes the front delay and takes a measurement.
5. The Product selects Rear Input with the front terminals isolated.
6. The Product executes the rear delay and takes a measurement
7. The displayed result is the combination of the two measurements.
The Product waits with Rear selected (front is isolated) for next trigger.
4W Tru Ohm Scan Mode (Tru Ohms Ratio)
When you select 4W Tru mode in Resistance (Ohms), the Scan modes above
(Front - Rear, Front / Rear, and (Front - Rear) / Rear) are configured uniquely in
a mode Fluke Calibration calls Tru Ohm Ratio, a feature also found in the Fluke
8508A Reference Multimeter. The Product applies a stimulus current of
alternating polarity through both resistors simultaneously, and the potential
difference measured across the resistors is scanned between the front and rear
terminals, see Figure 23. This measurement configuration is beneficial for lower
value resistance measurements between an unknown and a reference resistor,
and reduces self-heating (power) modulation that would otherwise result from
scanning the stimulus current between the two resistors under test. Tru Ohms
Ratio is only selectable if the ohms range is locked. If Auto range is selected, the
scan modes are greyed out and Tru Ohms Ratio is not available. See the screen
below.
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