Thermal measuring and testing – Temperature measurement – Combined with diverse art device
Reexamination Certificate
2003-09-22
2004-11-16
Lefkowitz, Edward (Department: 2859)
Thermal measuring and testing
Temperature measurement
Combined with diverse art device
C374S176000, C374S183000, C324S11700H, C324S127000, C340S595000
Reexamination Certificate
active
06817760
ABSTRACT:
BACKGROUND OF THE INVENTION
Transformer heating in current probes has always been a problem with respect to the customer's safety and the probe's reliability. Measuring higher currents at higher frequencies continues to push the envelope on what probes/amplifiers can provide. In the past, derating curves have been used to indicate the safe operating areas of the probe but could not detect situations in which a customer was exceeding the derating curves. The ability to constantly measure and monitor the temperature of the transformer allows control of the maximum temperatures that the probe can reach and limit potential damage to the probe as well as safety issues for customers. The below described invention disclosures a method for monitoring the transformer temperature in current probes.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a method of monitoring the temperature of a transformer winding in a current probe. The current probe includes a magnetic core having a multi-turn winding disposed there-around forming a probe transformer. A Hall Effect device is disposed within the magnetic core for generating a differential output signal for producing a current signal through the multi-turn winding. The current probe transformer temperature monitoring method determines an initial transformer temperature of the current probe as a function of the winding resistance of the transformer. A relative temperature of the Hall Effect device is also determined as a function of resistance change of the Hall Effect device. The initial transformer temperature and the relative Hall Effect device temperature are combined to produce a continuous transformer temperature indicative of the temperature of the transformer. The current signal to the multi-turn winding is removed when the continuous transformer temperature exceeds a threshold temperature value and a visual indication may be provided.
The initial transformer temperature determining step includes the steps of storing the thermal coefficient of copper, &agr;, an initial transformer temperature, T
0
, and a termination resistance, R
termination
, in memory. Digital values representative of an input voltage, Vin, to the multi-turn winding and an output voltage, Vout, from the multi-turn winding are generated and an initial probe resistance, R
0
, is calculated using the termination resistance and the digital values of the input and output voltages. The initial transformer temperature, T
probe
, is calculated using the function:
T
probe
=
T
0
+
1
α
(
R
termination
(
Vin
-
Vout
)
-
R
0
Vout
R
0
Vout
)
The relative temperature of the Hall Effect device determining step includes the steps of storing a thermal coefficient of resistance value of the Hall Effect device, &agr;
H
, a Hall Effect device bias voltage source value, V
Bias+
, and a resistance bias value, R
Bias
, in memory. A digital value representative of a voltage, V
Hall+
, across the Hall Effect device is generated and an initial Hall Effect device resistance value, R
Hall
, calculated using the function:
R
Hall
=
(
2
×
V
Hall
+
R
Bias
V
Bias
+
-
V
Hall
+
)
and stored in memory as R
Hall Init.
. Additional digital values representative of the voltage, V
Hall+
are generated and Hall Effect resistance values, R
Hall
, representing changes in the resistance of the Hall Effect device as a function of temperature are calculated. Changes in temperature of the Hall Effect device, &Dgr;T
probeHall
, are calculated using the function:
Δ
T
probeHall
=
1
α
H
(
R
Hall
-
R
Hall
Init
.
R
Hall
Init
.
)
temperature value.
Alternately, the first order equation may be modified to include first and second order terms, k
1
and k
2
, to increase the accuracy of the change in temperature calculation.
&Dgr;
T
probeHall
=k
1
(
R
Hall
−R
Hall Init.
)+
k
2
(
R
Hall
−R
Hall Init.
)
2
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.
REFERENCES:
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patent: 2464807 (1949-03-01), Hansen, Jr.
patent: 4327416 (1982-04-01), Jerrim
patent: 4623265 (1986-11-01), Poyser
patent: 4897584 (1990-01-01), Grutzmacher et al.
patent: 5493211 (1996-02-01), Baker
patent: 6042265 (2000-03-01), Kliman et al.
patent: 6139181 (2000-10-01), Olszowka
patent: 6204657 (2001-03-01), Stanley
patent: 6400131 (2002-06-01), Turner
patent: 6687636 (2004-02-01), Van Sant
patent: 2004/0100248 (2004-05-01), Mende
Crane, Jr. Albert S.
Dandy Jonathan S.
Mende Michael J.
Stevens Michael D.
Bucher William K.
Lefkowitz Edward
Pruchnic Jr. Stanley J.
Tektronix Inc.
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