IET Labs, Inc. RLC Digibridge 1693, User And Service Manual, Page: 67 / 171

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1693 RLC Digibridge
Operation
3.4.2 Test Voltage
The power-up test voltage is 1.0 volt rms, unless the
keyboard has been locked with some other choice.
There are a total of 255 choices: .005 to 1.275 V in
increments of .005 V. To program the test voltage:
1. Select ENTER with the [FUNCTION] key.
2. Enter the desired voltage in volts and press
[=][SHIFTT](VOLTAGE], in sequence as
follows. For example, to select 750 mV rms,
press:
[.][7][5][=][SHIFT][VOLTAGE]
The accuracy of the programmed source voltage is:
±[(5%+2mV)(1+0.001* f
2
)]
where f = value of test frequency in kHz.
The actual voltage across the DUT is never more than
the source voltage, and depends on the DUT imped-
ance and the source resistance of the Digibridge, for
the range in use. The DUT voltage is close to the
source voltage at the high-impedance end of each
measurement range and lower at the low-impedance
end. Normally, the smallest voltage across the DUT
(if its impedance is 6.25 ohms or more) will be 20%
of the source voltage; this is the case for resistors
measured at the low end of each range. Refer to Table
3-7 for details. (This table is similar to the table of
range constants in the specifications. However, the
extreme limits are given here, on ranges 1 and 4.)
For example, what is the voltage across the DUT if it
is a l µF capacitor. Assume the test frequency is 1 kHz,
the test voltage is 1.0 V, the CONSTANT VOLTAGE
indicator is NOT lit and the RANGE HELD indicator
is NOT lit. The Digibridge will measure on range 3,
with 1.0 V behind source resistance of 400 ohms. The
DUT reactance is 159 ohms and the voltage across
it is 370 mV.
For comparison, what is the voltage across the same
DUT if you select CONSTANT VOLTAGE (see para-
graph 3.4.3) or if range 4 is held. In either case, the
source, 1.0 V, is behind 25 ohms, The voltage across
the DUT is 988 mV.
Table 3-7: Autoranging Measurement Ranges and Source Resistance