Differential voltage measurement
View Patent ↗Measurement system and procedure suitable for measuring a voltage differential, the system comprising a measurement unit ( 1 ) having a first ground ( 10 ) as voltage reference and comprising a microcontroller ( 7 ) with an analog-digital converter ( 5 ), a sensor ( 2 ) having a second ground ( 20 ) as voltage reference, said second ground ( 20 ) being able to exhibit a potential difference with respect to the first ground ( 10 ), said measurement unit ( 1 ) having a first input ( 11 ) connected directly to the signal output ( 21 ) of the sensor ( 2 ), and a second input ( 12 ) connected directly to said second ground ( 20 ), the first and second inputs ( 11, 12 ) being linked to digital inputs ( 61, 62 ) of the microcontroller ( 7 ) through circuits for conditioning ( 31, 32, 41, 42 ) and analog-digital conversion ( 51, 52 ).
1. A measurement system for measuring a voltage differential, said system comprising:
a measurement apparatus ( 1 ) having a first ground ( 10 ) as voltage reference, said measurement apparatus comprising a microcontroller ( 7 ) and an analog-digital converter ( 5 ); and
a sensor ( 2 ) in electrical connection with the measurement apparatus, the sensor ( 2 ) having a second ground ( 20 ) as voltage reference, said second ground ( 20 ) configured to exhibit a potential difference with respect to the first ground ( 10 ), said sensor ( 2 ) having a voltage source (Vs) with a signal output ( 21 ),
said measurement apparatus ( 1 ) comprising a first input ( 11 ) connected directly to the signal output ( 21 ) of the sensor ( 2 ), a first conditioning circuit ( 31 , 41 ) connecting the first input to a first digital input ( 61 ) of the microcontroller ( 7 ), a second input ( 12 ) connected directly to said second ground ( 20 ), and a second conditioning circuit ( 32 , 42 ) connecting the second input to a second digital input ( 62 ) of the microcontroller ( 7 ), each of the first conditioning circuit ( 31 , 41 ) and the second conditioning circuit ( 32 , 42 ) entering an analog-to-digital converter ( 51 ) before terminating at a respective one of the first and second digital input
the first conditioning circuit ( 31 , 41 ), comprised of a first divider bridge, and the second conditioning circuit ( 32 , 42 ), comprised of a second divider bridge,
wherein said first and second conditioning circuits ( 31 , 41 , 32 , 42 ) comprise:
a first bias resistor (Rp) connected to a first bias potential (Vp) for biasing the first input ( 11 ),
a second bias resistor (Rp_gnd) connected to a second bias potential (Vp_gnd) for biasing the second input ( 12 ),
wherein a first input voltage (V 1 ) read on the first input ( 11 ) is conditioned by the first conditioning circuit ( 31 , 41 ) into a first conditioned voltage (Vax), and said first conditioned voltage (Vax) is then digitized by said analog-to-digital converter into a first digital value (Nax) provided to the first digital input ( 61 ) of the microcontroller ( 7 ),
wherein a second input voltage (Vgnd) read on the second input ( 12 ) is conditioned by the second conditioning circuit ( 32 , 42 ) into a second conditioned voltage (Vay), and said second conditioned voltage (Vay) is then digitized by said analog-to-digital converter into a second digital value (Nay) provided to the second digital input ( 62 ) of the microcontroller ( 7 ),
wherein the microcontroller determines and outputs a digital value (Ns) corresponding to a value of the voltage source (Vs) by means of the first digital value (Nax) and the second digital value (Nay) input to the microcontroller, a potential difference between the first and second grounds ( 10 , 20 ) being not present in the output digital value (Ns) even where the second input (Vgnd) is negative, and
wherein the microcontroller is configured to determine the digital value (Ns) corresponding to the value of the voltage source (Vs) by applying the first digital value (Nax) and the second digital value (Nay) to the formula:
Ns
=
Nax
(
Rs
+
Rin
+
Rp
)
Rp
-
Nay
(
Rin_gnd
+
Rp_gnd
)
Rp_gnd
+
Noff
in which:
Rs is the series resistance of the sensor ( 2 ),
Rin is the series resistance of the first conditioning circuit ( 31 ),
Rin_gnd is the series resistance of the second conditioning circuit ( 32 ),
Rp is the bias resistance of the first conditioning circuit ( 31 ),
Rp_gnd is the bias resistance of the second conditioning circuit ( 32 ), and
Noff is a constant offset value,
and in which Noff is determined by the microcontroller in accordance with the formula:
Noff
=
2
N
Vref
[
Vp_gnd
*
Kp_gnd
Ks_gnd
-
Kp
*
Vp
Ks
]
in which:
Ks
=
Rp
(
Rs
+
Rin
+
Rp
)
,
Kp
=
(
Rs
+
Rin
)
(
Rs
+
Rin
+
Rp
)
,
and
Ks+kp= 1,
Vref being a positive voltage reference of the analog-digital converter ( 5 ) of the measurement unit ( 1 ),
Vp being a first bias voltage,
Vp gnd being a second bias voltage,
Kp and Ks being, for the first conditioning circuit ( 31 ), the coefficients of the divider bridge formed by the resistors Rp, Rin and the resistor Rs present in the sensor, and
Kp_gnd and Ks_gnd being, for the second conditioning circuit ( 32 ), the coefficients of the divider bridge formed by the resistors Rp_gnd, Rin_gnd.
2. The measurement system as claimed in claim 1 , wherein the first and second bias voltages (Vp, Vp_gnd) are each derived from a reference voltage (Vref) of the analog-digital converter ( 5 ) of the measurement unit ( 1 ).
3. The measurement system as claimed in claim 2 , wherein the first and second bias voltages (Vp, Vp_gnd) are identical to the reference voltage (Vref) of the analog-digital converter ( 5 ) of the measurement unit ( 1 ).
4. The measurement system as claimed in claim 3 ,
wherein the first conditioning circuit ( 31 ) comprises a first foot resistor (Rpd), and
wherein the second conditioning circuit ( 32 ) comprises a second foot resistor (Rpd_gnd).
5. A method for measuring a voltage source, comprising:
providing a measurement unit ( 1 ) that includes a microcontroller ( 7 ) and a first ground ( 10 ) as voltage reference, and a sensor ( 2 ) having a second ground ( 20 ) as voltage reference, said second ground ( 20 ) configured to exhibit a potential difference with respect to the first ground ( 10 ), said sensor ( 2 ) having a voltage source (Vs) with a signal output ( 21 ),
said measurement unit ( 1 ) comprising a first input ( 11 ) connected directly to the signal output ( 21 ) of the sensor ( 2 ), a first conditioning circuit ( 31 , 41 ) connecting the first input to a first digital input ( 61 ) of the microcontroller ( 7 ), a second input ( 12 ) connected directly to said second ground ( 20 ), and a second conditioning circuit ( 32 , 42 ) connecting the second input to a second digital input ( 62 ) of the microcontroller ( 7 ), each of the first conditioning circuit ( 31 , 41 ) and the second conditioning circuit ( 32 , 42 ) entering an analog-to-digital converter ( 51 ) before terminating at a respective one of the first and second digital input
the first conditioning circuit ( 31 , 41 ), comprised of a first divider bridge, and the second conditioning circuit ( 32 , 42 ), comprised of a second divider bridge;
biasing the first input ( 11 ) by means of a first bias resistor (Rp) connected to a first bias potential (Vp);
biasing the second input ( 12 ) by means of a second bias resistor (Rp_gnd) connected to a first bias potential (Vp_gnd);
simultaneously acquiring voltages present on the first and second inputs of the measurement unit ( 1 ) as a first input voltage (V 1 ) and a second input voltage (Vgnd);
conditioning the acquired first input voltage (V 1 ) into a first conditioned voltage (Vax) by way of the first conditioning circuit ( 31 , 41 ), and digitizing said first conditioned voltage (Vax) into a first digital value (Nax) by way of said analog-to-digital converter, the first digital value (Nax) being provided to the first digital input ( 61 ) of the microcontroller ( 7 );
conditioning the acquired second input voltage (Vgnd) on the second input ( 12 ) into a second conditioned voltage (Vay) by way of the second conditioning circuit ( 32 , 42 ), and digitizing said second conditioned voltage (Vay) into a second digital value (Nay) by way of said analog-to-digital converter, the second digital value (Nay) being provided to the second digital input ( 62 ) of the microcontroller ( 7 ); and
determining, at the microcontroller, a digital value (Ns) corresponding to the value of the voltage source (Vs) by means of the first digital value (Nax) and the second digital value (Nay) input to the microcontroller, a potential difference between the first and second grounds ( 10 , 20 ) being not present in the output digital value (Ns) even where the second input (Vgnd) is negative,
wherein the microcontroller determines the digital value (Ns) corresponding to the voltage source (Vs) by the applying the first digital value (Nax) and the second digital value (Nay) to the formula:
Ns
=
Nax
(
Rs
+
Rin
+
Rp
)
Rp
-
Nay
(
Rin_gnd
+
Rp_gnd
)
Rp_gnd
+
Noff
wherein:
Rs is the series resistance of the sensor ( 2 ),
Rin is the series resistance of the first conditioning circuit ( 31 ),
Rin_gnd is the series resistance of the second conditioning circuit ( 32 ),
Rp is the bias resistance of the first conditioning circuit ( 31 ),
Rp_gnd is the bias resistance of the second conditioning circuit ( 32 ), and
Noff is a constant offset value,
and in which the microcontroller determines Noff by calculating the formula:
Noff
=
2
N
Vref
[
Vp_gnd
*
Kp_gnd
Ks_gnd
-
Kp
*
Vp
Ks
]
in which:
Ks
=
Rp
(
Rs
+
Rin
+
Rp
)
,
Kp
=
(
Rs
+
Rin
)
(
Rs
+
Rin
+
Rp
)
,
and
Ks+kp= 1,
Vref being a positive voltage reference of the analog-digital converter ( 5 ) of the measurement unit ( 1 ),
Vp being a first bias voltage,
Vp_gnd being a second bias voltage,
Kp and Ks being, for the first conditioning circuit ( 31 ), the coefficients of the divider bridge formed by the resistors Rp, Rin and the resistor Rs present in the sensor, and
Kp_gnd and Ks_gnd being, for the second conditioning circuit ( 32 ), the coefficients of the divider bridge formed by the resistors Rp_gnd, Rin_gnd.
6. The measurement method as claimed in claim 5 , wherein the first and second bias voltages (Vp,Vp_gnd) are identical to the reference voltage (Vref) of the analog-digital converter ( 5 ) of the measurement unit ( 1 ) such that
Vp=Vp _ gnd=V ref
and in which
Noff
=
2
N
[
Rin_gnd
Rp_gnd
-
Rs
+
Rin
Rp
]
.
7. The measurement method as claimed in claim 5 , wherein, the microcontroller of the measurement unit carries out an initial calibration operation, said initial calibration operation comprising:
carrying out a measurement on at least one gauge sensor, and determining therefrom an absolute correction coefficient and a proportional correction coefficient; and
calculating a corrected digital image (Ns_corr) from the digital value (Ns) corresponding to the value of the voltage source (Vs) according to the formula:
Ns _corr= A×Ns+B.
8. The measurement method as claimed in claim 6 , wherein, the microcontroller of the measurement unit carries out an initial calibration operation, said initial calibration operation comprising:
carrying out a measurement on at least one gauge sensor, and determining therefrom an absolute correction coefficient and a proportional correction coefficient; and
calculating a corrected digital image (Ns_corr) from the digital value (Ns) corresponding to the value of the voltage source (Vs) according to the formula:
Ns _corr= A×Ns+B.