Valhalla Scientific 4300C, Operation Manual

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25
Measurement Modes and Functions
The main characteristic of the 4300C is the 4-wire resistance measurements. In addition to standard
measurements, the 4300C includes the TCM and HLC modes. These features may significantly ease time
and cost of temperature sensitive and automated selection applications.
Standard Measurement Mode
In the standard measurement mode, the instrument simply measures the value of the applied load using
a 4-wire configuration. This configuration eliminates errors normally caused by test lead and contact
resistances. In many applications the contact resistance can exceed the value of the load by several orders
of magnitude. The 4300C bypasses this potential error source by providing two terminals of constant
current and an additional two terminals for high impedance voltage measurement. The result is a fast,
accurate resistance measurement of the load, independent of the resistance of the current carrying leads.
“TCM” - Temperature Compensated Measurement Mode
Valhalla Engineers are pioneers in the technology of accurate measuring devices using recognized
formulas that compensate for measurement inaccuracies because of environmental changes. The TCM
feature simulates a constant ambient temperature chamber for materials which are normally subject to
varying ambient temperatures. When in the TCM mode, the temperature sensor (Omni Compensator),
automatically senses the ambient temperature and compensates the reading to indicate what the actual
resistance value should be in a controlled environment (usually 20°C). The compensated value is
calculated with the following equation:
∆R
𝑅
!
= α∆T
The variation of resistance (ΔR) divided by the initial resistance (R
0
), is equal to the temperature coefficient
of the material (α) multiplied by the variation of temperature (ΔΤ).
Expressed in terms of the resistance:
𝑅 − 𝑅
!
𝑅
!
= 𝛼(𝑇 − 𝑇
!
)
or 𝑅 = 𝑅
!
[1 + 𝛼(𝑇 − 𝑇
!
)]
To better understand our uses of the equation, we will now express it in terms of our application.
𝑅
"
= 𝑅
#
[1 + 𝛼(𝑇
$
− 𝑇
%
)]
Where R
C
is the compensated value, R
M
is the measured resistance, T
A
is the ambient temperature and T
R
is the temperature reference. The compensated resistance is therefore calculated as follows:
𝑅
#
=
𝑅
"
1 + 𝛼(𝑇
$
− 𝑇
%
)
The user can select from a list of temperature coefficients and temperature references. The list is based
on the most used values. The user can also customize these settings with unique values.
Once the temperature coefficient and the temperature reference are set, the instrument’s task is to
measure the load resistance and the ambient temperature. After all the variables are determined, the
4300C automatically calculates the compensated resister value.