VCS101, VCS103, VCS401
Vishay Foil Resistors
High Precision Bulk Metal® Foil Power Current Sensing Resistors
with 3 A and 15 A Maximum Current, TCR to ± 15 ppm/°C
from 0.005
FEATURES
NEW
Temperature coefficient of resistance (TCR):
± 20 ppm/°C (available to ± 15 ppm/°C)
Resistance tolerance: to ± 0.1 %
Resistance range: 0.005
to 0.25 (for higher or
lower values please contact us)
INTRODUCTION
Model VCS101, VCS103 and VCS401 resistors are available in 2
configurations. This Bulk Metal® resistor can serve as a low ohm,
high power resistive shunt or as a medium power current sensing
resistor. Resistors are non-insulated.
Power rating: to 1.5 W at + 25 °C (free air)
Maximum current: to 15 A
Maximum operating temperature: + 175 °C
Load life stability: ± 0.5 % at 25 °C, 2000 h at rated power
The art of current sensing calls for a variety of solutions based on
application requirements. Current sensing is best achieved with a
Kelvin connection, which removes the unwanted influences of lead
resistance and lead sensitivity to temperature. Other requirements
such as high stability and short thermal stabilization time when the
Vishay Foil Resistors are not restricted to standard values;
specific “as required” values can be supplied at no extra cost or
delivery (e.g. 0R123 vs. 0R1)
power changes may dictate
a
special resistor design.
Non-inductive, non-capacitive design
4 leads for Kelvin connection
High-precision resistors used for current sensing are usually low
ohmic value devices suitable for four terminal connections. Two
terminals, called “current terminals”, are connected to conduct
electrical current through the resistor, while voltage drop VS is
measured on the other two terminals, called “sense” or “voltage
drop” terminals. According to Ohm’s law, the sensed voltage drop
VS divided by the known resistance RS gives the sensed current
IS. The accuracy of measurement depends on the stability of ohmic
resistance RS between the nodes, i.e. the points of connection of
the sense leads. Since the voltage leads feed into an “infinite”
resistance circuit, there is no current flowing through the voltage
terminals and, therefore, no IR drop in the voltage sense leads.
Thus, the four-terminal system eliminates the voltage drop errors
originated in the leads when the voltage terminations are
connected close to the resistance element (excluding significant
portions of the leads that carry the current).
Rise time: 1.0 ns effectively no ringing
Thermal EMF: 0.05 µV/°C typical
Voltage coefficient: < 0.1 ppm/V
Non-inductive: 0.08 µH
Terminal finish: lead (Pb)-free or tin/lead alloy*
Prototype quantities available in just 5 working days or sooner.
For more information, please contact foil@vishaypg.com
For better performances, see VCS201, VCS202 and VCS301,
VCS302 datasheets or contact application engineering
Real life resistors exhibit two types of reversible changes:
This arrangement, called a “Kelvin connection”, reduces, especially
for low ohmic resistance values, a measurement error due to the
resistance of the lead wires and the solder joints as the sensing is
performed inside the resistor, in or close to the active resistive bulk
metal foil element. Of the commonly used methods of measuring the
magnitude of electrical current, this current sensing resistor method
provides the most precise measurement. According to Ohm’s law,
V = IR, the voltage drop measured across a resistor is proportional to
the current flowing through the resistor. With the known and stable
value of the resistance R, the voltage drop sensed on the resistor
indicates the intensity of the current flowing through it.
Assuming an ideal current sense resistor that doesn’t change
its resistance value when there is a change in the magnitude
of the current or a change in environmental conditions, like
the ambient temperature or self heating, the measured voltage
drop will yield a precise value of the current: I = V/R. But with
a real-life resistor, such as a metal film resistor or a manganin
bar, a change in current intensity (and in the dissipated power)
will cause a change in the resistor's value which will involve a
thermal transient period taking a few seconds or longer to
stabilize. Therefore, the key to a fast and precise measurement
of current is the use of a real life current sensing resistor
which approaches, as closely as possible, an ideal resistor.
That is, a resistor that is not influenced by changes in the
magnitude of the current flowing through it nor by changes in
ambient temperature or any other environmental condition.
1. When they are cooled or heated by a changing ambient
temperature, and
2. By self-heating due to the power they have to dissipate (Joule
effect).
When a high precision is required, these two effects induce a change
in the resistive element's temperature, Ta due to ambient and Tsh
due to self heating, both of which must be considered.
The ambient temperature changes slowly, and all parts of a resistor
follow uniformly the change of the ambient temperature, but the effect
of the dissipated power is different. The temperature of the resistive
element - the active part of the resistor - will change rapidly with the
change of the intensity of current. The power it has to dissipate will
change proportionally to the square of the current and a rapid increase
in current will cause a sudden increase in the temperature of the
resistive element and in the heat that must be dissipated to the
ambient air. These two effects of resistance changes are quantified by
TCR - Temperature Coefficient of Resistance and by PCR - Power
Coefficient of Resistance (called also “Power TCR”).
Our applications engineering department is prepared to advise
and to make recommendations. For non-standard technical
requirements and special applications, please contact us.
* Pb containing terminations are not RoHS compliant, exemptions may apply
Document Number: 63016
Revision: 5-Jun-12
For any questions, contact: foil@vishaypg.com
www.vishayfoilresistors.com
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