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US 20130249575A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2013/0249575 A1
HERTES
(54)
(43) Pub. Date:
DEVICE AND METHOD FOR MEASURING A
VALUE OF A RESISTOR
Publication Classi?cation
(5 1) Int. Cl.
G01R 2 7/02
(52) US. Cl.
(71) Applicant: CONTINENTAL AUTOMOTIVE
GMBH, HANNOVER (DE)
Sep. 26, 2013
(2006.01)
CPC .................................... .. G01R 27/02 (2013.01)
(72)
Inventor:
VOLKER HERTES, HAGELSTADT
(DE)
(73)
USPC ........................................................ .. 324/711
(57)
ABSTRACT
A device for measuring the value of a resistor has a ?rst RC
element With a ?rst time constant and a second RC element
With a second time constant. The ?rst RC element has a ?rst
capacitor and a resistor. The second RC element has a second
capacitor and the resistor to be measured. An evaluation cir
Assigneez CONTINENTAL AUTOMOTIVE
GMBH HANNOVER (DE)
(21) APPL NO; 13/849,101
cuit charges the ?rst
second capacitors to 'a ?rst and a
second voltage, respectively, and m1t1ates their discharge.
The evaluation circuit measures the time that elap ses from the
(22)
Filed;
Man 22, 2013
(30)
start of the discharge to the instant at Which the voltages
across the capacitors are equal, and determines the value of
Foreign Application Priority Data
Mar. 22, 2012
\ii
the resistor from the values. In the event that the ?rst time
constant is larger than the second time constant, the ?rst
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voltage is smaller than the second voltage, and vice versa.
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Patent Application Publication
Sep. 26, 2013
US 2013/0249575 A1
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Sep. 26, 2013
US 2013/0249575 A1
DEVICE AND METHOD FOR MEASURING A
VALUE OF A RESISTOR
CROSS-REFERENCE TO RELATED
APPLICATION
[0001] This application claims the priority, under 35 U.S.C.
§119, of German patent application DE 10 2012 204 569.4,
?led Mar. 22, 2012; the prior application is herewith incor
porated by reference in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002]
The value of a resistor often serves as a measure of
the temperature, for example of a heating element. Conse
quently, the resistance needs to be measured in order to deter
mine the temperature. Although in principle this can be
the ?rst time constant is greater than the second time
constant, the ?rst voltage is smaller than the second
voltage, and vice versa.
[0011] In other Words, the objects of the invention are
achieved by Way of a device for measuring the value of a
resistor, having a ?rst RC element, Which has a ?rst time
constant and is formed from a ?rst capacitor and a further
resistor, Which is connected in parallel With the ?rst capacitor.
In addition, the device has a second RC element, Which has a
second time constant and is correspondingly formed from a
second capacitor and the resistor to be measured, Which is
connected in parallel With the second capacitor. The capaci
tors are charged to different voltages by means of an evalua
tion circuit, Wherein the ?rst time constant is larger than the
second time constant When the ?rst voltage is smaller than the
second voltage, and vice versa. If appropriate sWitching
means ensure at a particular instant that the capacitors can
only discharge via the resistors assigned thereto, there is a
accomplished by Way of the quotient of the voltage drop
particular instant at Which the voltages across the tWo capaci
across the resistor and the current ?owing through the resis
tors are equal. This instant can be detected. The value of the
resistor to be measured can be calculated from knoWledge of
this instant and of the values of the tWo capacitors and the
further resistor, and also of the ratio of the tWo voltages to
tor, this is complex and expensive, since a speci?c shunt
resistor is usually required for measuring the current. HoW
ever, the value of the shunt has an upper limit for reasons of
poWer loss, and the physical siZe of the shunt limits the value
doWnWards. The current-measuring circuit must be designed
in a correspondingly sensitive manner With corresponding
concessions in terms of accuracy. Moreover, large resistors
tend to exhibit loWer reliability for the solder joints. In the
case of loads With a ?xed ground connection, in Which the
supply of poWer is controlled by connecting and disconnect
ing the battery voltage, the shunt must be on the battery side
of the load and the battery-referenced current-measuring sig
nal must be converted in a complex manner into a ground
referenced signal so that it can be processed further.
SUMMARY OF THE INVENTION
Which the capacitors are charged.
[0012] In accordance With an added feature of the inven
tion, a voltage divider is connected betWeen the ?rst and
second capacitors and a voltage source for charging the
capacitors, and Wherein the evaluation circuit is con?gured to
connect one of the ?rst and second capacitors to the voltage
source via a ?rst controllable sWitch and to connect the
respectively other capacitor to the voltage source via the ?rst
sWitch and the voltage divider, and Wherein the voltage
divider is con?gured to draW no current While the ?rst and
second capacitors are discharging.
[0013] In accordance With an advantageous feature of the
invention, a ?rst sWitch connected at an input of the voltage
[0003]
It is accordingly an object of the invention to provide
a method and a device Which overcome a variety of disadvan
tages of the heretofore-known devices and methods of this
general type and Which provides for a novel a device and a
method for measuring the value of a resistor.
[0004]
With the foregoing and other objects in vieW there is
provided, in accordance With the invention, a device for mea
suring a value of a resistor, comprising:
[0005] a ?rst RC element having a ?rst time constant, the
?rst RC element including a ?rst capacitor and a further
resistor connected in parallel With the ?rst capacitor;
[0006]
a second RC element having a second time con
stant, the second RC element including a second capaci
tor and the resistor to be measured connected in parallel
With the second capacitor;
[0007]
an evaluation circuit connected to the ?rst and
second capacitors and being con?gured:
[0008] to charge the ?rst and second capacitors to a
?rst voltage and a second voltage, respectively, and to
initiate a discharge thereof through only the further
resistor or the resistor to be measured;
[0009]
to measure a time that elapses from a start of a
discharge of the ?rst and second capacitors to an
instant at Which the voltages across the ?rst and sec
ond capacitors are equal; and
[0010] to determine the value of the resistor to be
measured from the values, Wherein, in an event that
divider and a second sWitch connected at an output of the
voltage divider are driven by the evaluation circuit so as to be
open during the discharge process.
[0014] With the above and other objects in vieW there is
also provided, in accordance With the invention, a method of
measuring a value of a resistor. The method Which comprises:
[0015] providing a measuring device as outlined above
and charging the ?rst capacitor of the ?rst RC element to
a ?rst voltage and charging the second capacitor of the
second RC element to a second voltage;
[0016] if the ?rst time constant is greater than the second
time constant, the ?rst voltage is smaller than the second
voltage, and vice versa, and a ratio of the ?rst voltage to
the second voltage is l/K;
[0017] With an evaluation circuit, initiating a discharge
of the capacitors and measuring a time interval that
elapses from a start of the discharge of the capacitors to
an instant at Which the ?rst and second voltages across
the capacitors are equal, and determining a value of the
resistor to be measured from the values of the ?rst and
second capacitors, of the further resistor, the ratio of the
?rst voltage to the second voltage, and the measured
time.
[0018]
In accordance With a concomitant feature of the
invention, the evaluation circuit is con?gured to determine
the value of the resistor according to the formula
Sep. 26, 2013
US 2013/0249575 Al
1
TORRCR
capacitors CR, CL and the voltage divider l/K is also inter
rupted, With the result that the capacitors can discharge only
through the resistors RR, RL assigned thereto in the tWo RC
elements.
wherein:
[0019]
RL is the value of the resistor to be measured;
[0020]
[0021]
CL is the capacitance of the second capacitor;
T0 is the measured time interval;
[0022]
[0023]
RR a resistance of the ?rst resistor;
CR is a capacitance of the ?rst capacitor;
[0024]
K is a ratio of the ?rst voltage to the second
voltage.
[0025] Other features Which are considered as characteris
tic for the invention are set forth in the appended claims.
[0026]
Although the invention is illustrated and described
herein as embodied in a device and method for measuring the
value of a resistor, it is nevertheless not intended to be limited
to the details shoWn, since various modi?cations and struc
[0033] The voltages VR and VL across the capacitors are
supplied to the evaluation circuit Control and, for example,
have a pro?le as shoWn in FIG. 2. At the instant TO, after the
sWitch-off operation at the instant tOFF, the tWo voltages VR
and VL have the same value, and this is detected by the
evaluation circuit Control. The evaluation circuit Control has
a chronometric device in order to record the time period TO.
The value of the resistor RL can be determined from the
knoWn values of the ?rst capacitor CR, of the further resistor
RR, of the second capacitor CL, the determined time period TO
and the ratio l/K of the tWo voltages VR and VL to Which the
tWo capacitors Were initially charged, according to the for
mula
tural changes may be made therein Without departing from
the spirit of the invention and Within the scope and range of
equivalents of the claims.
[0027] The construction and method of operation of the
l
TORRCR
invention, hoWever, together With additional objects and
[0034]
advantages thereof Will be best understood from the folloW
ing description of speci?c embodiments When read in con
method according to the invention alloW indirect current mea
nection With the accompanying draWings.
The device according to the invention and the
surement using a complex and expensive ampli?er circuit
consisting of shunt, operational ampli?er and feedback net
Work to be omitted. Likewise, quantitative determination of
BRIEF DESCRIPTION OF THE SEVERAL
VIEWS OF THE DRAWING
[0028]
FIG. 1 is a basic circuit illustration of a device
according to the invention; and
[0029] FIG. 2 graph shoWing the pro?le of the voltages
across the tWo capacitors.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring noW to the ?gures of the draWing in detail
and ?rst, particularly, to FIG. 1 thereof, a ?rst RC element is
formed from a ?rst capacitor CR and a further resistor RR,
Which is connected in parallel With the ?rst capacitor CR. A
second RC element is formed from a second capacitor CL and
the resistor RL to be measured. The tWo capacitors CR, CL are
connected to a voltage source VQ, and are charged to a par
ticular voltage, by operation of a ?rst sWitch SW1. In this case
the value of said voltage is not important, rather only the ratio
of the ?rst voltage VR across the ?rst capacitor CR to the
second voltage VL across the second capacitor CL. This is
indicated by a voltage divider symbol l/K, Which represents
a circuit by Which the voltage of the voltage source VQ is
divided by the factor K. This can be realiZed With a simple
voltage divider having resistors; hoWever, it can also be of
more complex design.
[0031] The voltage divider l/K is con?gured such that in
the event that the capacitors CR, CL are discharging, no cur
rent can ?oW via the voltage divider l/K, but rather the capaci
tors CR, CL can discharge only via the resistor RR, RL respec
tively assigned thereto. As is shoWn schematically in FIG. 1,
this can be accomplished by means of corresponding
sWitches SWR, SWL, Which can be controlled by the evalua
tion circuit Control, at the input and output of the voltage
divider l/K.
the voltage across the resistor is not necessary. In this case the
measurement result is independent not only of the voltage to
be applied by the voltage source VQ but also of the residual
resistances of the closed sWitches SW, SWR, SWC,Wh1Ch are
usually realiZed by transistors in Which the sWitch-on resis
tances are highly dependent on temperature and current.
1. A device for measuring a value of a resistor, comprising:
a ?rst RC element having a ?rst time constant, said ?rst RC
element including a ?rst capacitor and a further resistor
connected in parallel With said ?rst capacitor;
a second RC element having a second time constant, said
second RC element including a second capacitor and the
resistor to be measured connected in parallel With said
second capacitor;
an evaluation circuit connected to said ?rst and second
capacitors and being con?gured:
to charge said ?rst and second capacitors to a ?rst volt
age and a second voltage, respectively, and to initiate
a discharge thereof through only said further resistor
or the resistor to be measured;
to measure a time that elapses from a start of a discharge
of said ?rst and second capacitors to an instant at
Which the voltages across said ?rst and second capaci
tors are equal; and
to determine the value of the resistor to be measured
from the values, Wherein, in an event that the ?rst time
constant is greater than the second time constant, the
?rst voltage is smaller than the second voltage, and
vice versa.
2. The device according to claim 1, Which further com
prises a voltage divider connected betWeen said ?rst and
second capacitors and a voltage source for charging said
capacitors, and Wherein said evaluation circuit is con?gured
As can be seen in FIG. 2, at an instant tOFF the
to connect one of said ?rst and second capacitors to said
voltage source via a ?rst controllable sWitch and to connect
sWitches SW, SWR, SWL are opened by the evaluation circuit
Control, Which ensures that the connection betWeen the
the respectively other capacitor to said voltage source via said
?rst sWitch and said voltage divider, and Wherein said voltage
[0032]
Sep. 26, 2013
US 2013/0249575 A1
divider is con?gured to draW no current While the ?rst and
second capacitors are discharging.
3. The device according to claim 2, Which comprises a ?rst
sWitch connected at an input of said voltage divider and a
second sWitch connected at an output of said voltage divider,
Wherein said ?rst and second sWitches are connected to said
evaluation circuit and said evaluation circuit is con?gured to
open said sWitches during the discharge process.
4. A method of measuring a value of a resistor, Which
comprises:
from a start of the discharge of the capacitors to an
instant at Which the ?rst and second voltages across the
capacitors are equal, and determining a value of the
resistor to be measured from the values of the ?rst and
second capacitors, of said further resistor, the ratio of the
?rst voltage to the second voltage, and the measured
time.
5. The according to claim 4, Wherein said evaluation circuit
is con?gured to determine the value of the resistor according
to the formula
providing a ?rst RC element, formed of a ?rst capacitor and
a further resistor and having a ?rst time constant, and
charging the ?rst capacitor to a ?rst voltage;
providing a second RC element, formed of a second
capacitor and the resistor to be measured and having a
second time constant, and charging the second capacitor
to a second voltage;
if the ?rst time constant is greater than the second time
constant, the ?rst voltage is smaller than the second
voltage, and vice versa, and a ratio of the ?rst voltage to
the second voltage is l/K;
With an evaluation circuit, initiating a discharge of the
capacitors and measuring a time interval that elapses
1
TORRCR
Wherein:
RL is the value of the resistor to be measured;
CL is the capacitance of the second capacitor;
T0 is the measured time interval;
RR a resistance of the ?rst resistor;
CR is a capacitance of the ?rst capacitor;
K is a ratio of the ?rst voltage to the second voltage.
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