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Instrument Functions

In the SETUP menu, use the arrow keys

to se-

lect the GUARD function, press the knob

(editing mode)

and select the desired setting via knob. Press the knob

again to confirm the selection.

The HM8118 GUARD function is not comparable to the
4TP function (= Four Terminal Pair) of other measuring in-
strument manufacturers. For the 4TP function, the mea-
surement current is returned through the test lead shield.
The electromagnetic radiation of the supply and return
conductor nearly override each other which for the most
part resolves the issue of electromagnetic coupling. This
does not work for the Kelvin test lead provided with the
R&S®HM8118, as this is not properly converted (the shields
would have to be short-circuited preferably close to the

test point). The HM8118 uses a 5 terminal configuration /

5T and does not support the 4TP function.

7.1.11 Deviation DEV_M

You can use the DEV_M function to turn on or off (OFF)
the display of the measurement deviation of the main dis-

play (Main) in Δ % (percent) or Δ ABS (absolute) as applied

to the reference value REF_M. In the SETUP menu, use the
arrow keys

to select the DEV_M function to

set the display for the measurement deviation, press the
knob

(editing mode) and select the desired setting via

knob. Press the knob again to confirm the selection. For

more information about the measurement value deviation,
see chapter 6.

7.1.12 Reference REF_M

You can use the REF_M function to save the measure-
ment value as a reference value in the reference memory
M (Main). You can choose one of the following as unit
for the measurement value: H, mH, µH, nH, F, mF, µF, nF,

pF, Ω, mΩ, kΩ, MΩ, or S, kS, mS, µS, nS, pS. In the SE

TUP menu, use the arrow keys

to select the

REF_M function to set the reference value, press the knob

(editing mode) and select the desired reference value

via knob. By pressing the knob again, you can activate the
manual value input via numeric keypad. A value input win-
dow will be opened. You can use the numeric keys to en-

ter a value. After entering the value via keypad, confirm the

entry by pressing the ENTER key or by pressing the knob

again. As long as this field is activated, you can also use

the TRIG key

to accept the value of the DUT (= Device

Under Test). For more information about the reference va-
lue, see chapter 6.

7.1.13 Deviation DEV_S

You can use the DEV_S function to turn on or off (OFF) the

display of the secondary value display (Sub) in Δ % (per

cent) or Δ ABS (absolute) as applied to the reference value

It is recommended to use the GUARD function if measurement
adapters with high capacity (e.g. R&S®HZ184) are used. If the
DUT exhibits impedances of more than 25kΩ at frequencies of
more than 100kHz, is is also recommended to use the GUARD
function.

REF_S. In the SETUP menu, use the arrow keys

to select the DEV_S function to set the display for the

measurement deviation, press the knob

(editing mode)

and select the desired setting via knob. Press the knob

again to confirm the selection. For more information about

the measurement value deviation, see chapter 6.

7.1.14 Reference REF_S

You can save a measurement value of the dissipation fac-
tor or the quality factor (quality) as reference value in the
reference memory S. You can choose one of the following

as unit for the measurement value: Ω, mΩ, kΩ, MΩ, S,

kS, mS, µS, nS, pS or °. In the SETUP menu, use the ar-
row keys

to select the REF_M function to

set the reference value, press the knob

(editing mode)

and select the desired reference value via knob. By pres-
sing the knob again, you can activate the manual value in-
put via numeric keypad. A value input window will be ope-
ned. You can use the numeric keys to enter a value. After

entering the value via keypad, confirm the entry by pres

sing the ENTER key or by pressing the knob again. As long

as this field is activated, you can also use the TRIG key

to accept the value of the DUT (= Device Under Test). For
more information about the reference value, see chapter 6.

7.1.15 CONSTANT VOLTAGE CST V

The CST V function allows you to turn the constant voltage
(AC) on (ON) or off (OFF). Due to the source resistance,

some test require the use of a specific measurement vol

tage which is not possible with the regular source resis-
tance of the respective measurement range. In the SETUP
menu, use the arrow keys

to select the CST V

function to activate the constant voltage, press the knob

(editing mode) and select the desired setting via knob.

Press the knob again to confirm the selection.

If the constant voltage is activated (ON), the source

resistance is preset to 25 Ω. The voltage applied to the

component will be nearly constant for all components

whose impedance is substantially greater than 25 Ω. If the

constant voltage mode is activated for the bridge, the
measurement range changes (depending on the
impedance of the connected component) to prevent
overloading the bridge. However, the accuracy is reduced
by the factor of 2 in the constant voltage mode. The
following table shows the impedance measurement
ranges when the constant voltage mode is activated (CST
V ON):

The constant voltage (CST V function) must be switched on for
measurements with BIAS bias current or external BIAS preload.

Measure-

ment Range

Source

Resistance

Component

Impedance

25 Ω

10.0 µΩ to 3.0 Ω

25 Ω

3.0 Ω to 100.0 Ω

25 Ω