OPERATION
2-7
autorange to range 0 (or range 1 for 100 kHz) and then autorange 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 range hold. The present measurement range can be held
by simply pressing the [Range Hold] key. The LED above the [Range Hold] key
indicates that the unit is in range hold. A measurement range can also be directly
entered from the ENTRY display. Select the ENTRY display using the [Display]
key, then press [Range 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] key. Use the [Display] key to return to the desired
display. The range hold LED will be on. If an invalid range is entered, the unit 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 100 kHz (SR720 only). If
this is attempted the unit will beep and display an 'r-f Error' (range - frequency
error).
To return the unit to autoranging mode, simply press the [Range Hold] key.
If the impedance of a part is more than 100 times the nominal value for the range,
the instrument indicates an 'ovEr rAnGE' (overrange) error. If this occurs, choose
a more appropriate range for the measurement. Measurement accuracy is
reduced if a component is measured outside of its optimal range. The accuracy of
an out-of-range measurement is as follows: for each factor of 2 outside of the
nominal range, the total error increases by the basic error. For example, if a part
is 4 times greater than the nominal range (2 factors of 2), then the total error will
be the basic ac 2 x the basic accuracy. In this case, the total error
increases to 3 x the basic error. For more information, see the accuracy section.
CONSTANT VOLTAGE
Occasionally, a test will require using a specific drive voltage that is not possible
using the normal source resistance for that measurement range. In these cases,
use the [Cons Volt] key to set the source impedance to a fixed 25
Ω
. The voltage
across the DUT will be almost constant for all devices with impedances
substantially larger than 25
Ω
. When the unit is in constant voltage mode, the
measurement ranges change to avoid overloading the unit. However, it also
reduces the accuracy of the measurement by a factor of 2. See the accuracy
section for more detail. The table below lists the impedance ranges when using
Constant Voltage.
Measurement Range and Impedance Range
Meas
Range
Source R
Resistance
Inductance
Capacitance
3
25.0
Ω
10
µΩ
-
0.0001
µ
H -
99999
µ
F -
360
Ω
57/f H
442/f
µ
F
2
25.0
Ω
360
µΩ
-
57/f H -
442/f mF -
5.76 k
Ω
917/f H
27.6/f
µ
F
1
25.0
Ω
5.76 k
Ω
-
917/f H -
27.6/f
µ
F -
90.0 k
Ω
14324/f H
1.77/f
µ
F
0
25.0
Ω
90.0 k
Ω
-
14324/f H -
1.77/f
µ
F -
2000 M
Ω
99999H
0.00001 pF
f is test
frequency
