CN101251399B - High input impedance differential pre-amplifier circuit of ultrasonic flowmeter - Google Patents
High input impedance differential pre-amplifier circuit of ultrasonic flowmeter Download PDFInfo
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- CN101251399B CN101251399B CN2008100527688A CN200810052768A CN101251399B CN 101251399 B CN101251399 B CN 101251399B CN 2008100527688 A CN2008100527688 A CN 2008100527688A CN 200810052768 A CN200810052768 A CN 200810052768A CN 101251399 B CN101251399 B CN 101251399B
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- resistance
- operational amplifier
- circuit
- integrated operational
- amplifier circuit
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Abstract
The invention relates to a high input impedance differential motion preamplifier circuit for an ultrasonic flowmeter, which comprises a high voltage protection circuit, a CMRR alignment circuit, and an amplifying circuit consisting of an integrated operational amplifier. The input signal from an ultrasonic probe is inputted into the high voltage protection circuit through an input signal terminal,the high voltage protection circuit is directly or indirectly connected with the CMRR alignment circuit, the CMRR alignment circuit can regulate the resistance balance of the preamplifier circuit toensure the high attenuation of a common mode signal, and the AC input impedance of the preamplifier is improved through the positive feedback characteristic of the amplifier. The high input impedancedifferential motion preamplifier circuit for the ultrasonic flowmeter has the advantages of obtaining a high input voltage signal from the probe and absorbing little power from the probe, and consequently ensuring the improved measuring accuracy of the whole machine.
Description
Technical field
The present invention relates to a kind of instrument and meter for automation, particularly a kind of high input impedance difference preliminary amplifier circuit of ultrasonic flow meter.
Background technology
The pre-amplification circuit of the employed probe interface of current ultrasonic flow meter all uses simple interface circuit, and no matter this circuit adopts discrete component or integrated transporting discharging, and the input impedance of the circuit that they are formed generally all is no more than 500k Ω, and does not adjust CMRR.The defective of this simple designs mainly contains 3 points: the one, ultrasonic emitting signal and received signal are arranged on the ultrasonic probe, and wherein transmitted tens of volts or hundreds of volt must could be protected prime amplifier with the protective resistance step-down of 50k～300k Ω; This protective resistance will with the input impedance dividing potential drop of amplifier, the ultrasound wave received signal of the ultrasonic probe output that decayed to a great extent.The 2nd, in prime amplifier input impedance during greater than 100k Ω, do not adjust CMRR again, certainly will make a part of common mode interference signal change the differential mode interference signal into, become the amplification target of back amplifier in amplifier input terminal, for flowmeter is introduced very big mushing error, for example civil power mushing error.The 3rd, if direct current input impedance is according to after exchanging input impedance and being enhanced, with increase prime amplifier the time float, interchange interference magnitude that temperature is floated.
Above-mentioned 3 is open question all the time in the current ultrasonic flow meter product, and they are not high all the time main causes of precision of ultrasonic flow meter.
Summary of the invention
Deficiency in view of the prior art existence, the invention provides a kind of interchange input impedance that utilizes positive feedback loop to strengthen preamplifier circuit, increase the CMRR potentiometer in addition again to guarantee the altitude decay of common-mode signal, make it to become the high input impedance difference preliminary amplifier circuit of ultrasonic flow meter.
The technical scheme that the present invention is adopted for achieving the above object is: a kind of high input impedance difference preliminary amplifier circuit of ultrasonic flow meter; it is characterized in that: comprise high tension protection circuit; CMRR adjusts circuit; integrated operational amplifier; described high tension protection circuit: comprise resistance R 1; resistance R 11; diode D1; diode D2; described CMRR adjusts circuit and comprises potentiometer R0; resistance R 2; resistance R 12; described integrated operational amplifier; comprise integrated operational amplifier circuit A1; integrated operational amplifier circuit A2; resistance R 6; resistance R 16; resistance R 3; resistance R 4; resistance R 5; resistance R 13; resistance R 14; resistance R 15; capacitor C 1; capacitor C 2; wherein two resistance R 1 and resistance R 11 and protection diode D1 and protection diode D2 form the amplitude limiter circuit of series loop form; diode D1; the two ends of diode D2 parallel connected in reverse phase are respectively through resistance R 2; resistance R 12 and integrated operational amplifier circuit A1; the in-phase input end of integrated operational amplifier circuit A2 links; potentiometer R0 directly or indirectly and high tension protection circuit and integrated operational amplifier circuit input end link; adjust the resistance of potentiometer R0; can change the overall symmetrical balance of each direct current resistance; be provided with resistance R 3 in the positive feedback loop of integrated operational amplifier circuit A1; resistance R 4; the T-network that resistance R 5 and capacitor C 1 are formed; wherein resistance R 3; resistance R 4 and resistance R 5 respectively have an end to be associated in together; in their other end; resistance R 4 ground connection; resistance R 3 connects the in-phase input end of A1; resistance R 5 meets the output terminal VO+ of integrated operational amplifier circuit A1 through capacitor C 1; the positive feedback loop of integrated operational amplifier circuit A2 is provided with resistance R 13; resistance R 14; the T-network that resistance R 15 and capacitor C 2 are formed; wherein resistance R 13; resistance R 14 and resistance R 15 respectively have an end to be associated in together; in their other end; resistance R 14 ground connection; resistance R 13 connects the in-phase input end of integrated operational amplifier circuit A2; resistance R 15 meets the output terminal VO-of integrated operational amplifier circuit A2 through capacitor C 2; be arranged on two negative feedback resistor R6 and the resistance R 16 of integrated operational amplifier circuit A1 and integrated operational amplifier circuit A2; gain with the control prime amplifier; the output terminal of resistance R 6 one termination integrated operational amplifier circuit A1 wherein; another termination inverting input; the output terminal of resistance R 16 1 termination integrated operational amplifier circuit A2, another termination inverting input.
The invention has the beneficial effects as follows: 1. utilize positive feedback loop to strengthen the interchange input impedance of preamplifier circuit; it is brought up in 10M～100M Ω scope; with the intrinsic standoff ratio of increasing, so amp.in can obtain the ultrasound wave input signal more than 90% from popping one's head in protective resistance.2. when improving interchange input impedance, can guarantee lower direct current input impedance.Greatly within 100k～500k Ω scope, to reduce the dc shift error.3. increase the CMRR potentiometer, guarantee the altitude decay of common-mode signal.This balancing circuitry design will make the value of CMRR be increased to more than the 60dB.
In a word, the high input impedance difference preliminary amplifier circuit of ultrasonic flow meter can obtain very high input voltage signal from probe, and but draw power is very little from probe, guarantees the raising of measuring accuracy.
Description of drawings
Fig. 1 is for application circuit of the present invention and as Figure of abstract.
Fig. 2 is a principle of the invention block scheme.
Embodiment
As shown in Figure 1, 2: a kind of high input impedance difference preliminary amplifier circuit of ultrasonic flow meter; also comprise high tension protection circuit; CMRR adjusts the amplifying circuit of circuit, integrated operational amplifier composition; wherein high tension protection circuit is connected with CMRR adjustment circuit, and CMRR adjusts circuit and is connected with the amplifying circuit that integrated operational amplifier is formed.High tension protection circuit comprises resistance R
1, R
11, diode D
1, D
2, CMRR adjusts circuit and comprises potentiometer R
0, resistance R
2, R
12, integrated operational amplifier comprises integrated operational amplifier circuit A
1, A
2, resistance R
6, R
16, R
3, R
4, R
5, R
13, R
14, R
15Capacitor C
1, C
2, input signal terminal V wherein
i +Pass through resistance R
1With diode D
1, D
2Reverse parallel connection one end, resistance R
2Connect resistance R
2The other end and resistance R 3 one ends, integrated operational amplifier circuit A
1In-phase input end connect resistance R
3The other end and resistance R
4, R
5An end connect resistance R
4Other end ground connection, resistance R
5The other end through capacitor C
1With integrated operational amplifier circuit A
1Output signal end V
O +Connect integrated operational amplifier circuit A
1Output signal terminal V
O +Pass through resistance R
6With integrated operational amplifier circuit A
1Inverting input connect input signal terminal V
i -Pass through resistance R
11With diode D
1, D
2The reverse parallel connection other end, potentiometer R
0Connect potentiometer R
0The other end passes through resistance R
12With integrated operational amplifier circuit A
2In-phase input end, resistance R
13Connect resistance R
13The other end and resistance R
14, R
15An end connect resistance R
14Other end ground connection, resistance R
15The other end through capacitor C
2With integrated operational amplifier circuit A
2Output signal terminal V
O -Connect integrated operational amplifier circuit A
2Output signal terminal V
O -Pass through resistance R
16With integrated operational amplifier circuit A
2Inverting input connect.
Two resistances of above-mentioned high tension protection circuit are in the resistance R of 50k～100k Ω
1And R
11With protection diode D
1And D
2The amplitude limiter circuit of forming the series loop form prevents that transmitting of the tens of volts of ultrasonic probe or hundreds of volts from puncturing amplifier A
1And A
2Input circuit.Diode D
1And D
2Indirect and the A of difference
1And A
2Input end link, make this maximum voltage signal of going into end be limited in ± 0.8V in, high tension protection circuit directly or indirectly and the amplifier input end link D
1And D
2Get the ordinary silicon diode.
Above-mentioned potentiometer R
0With resistor R
12, R
2The common CMRR of composition adjusts circuit, potentiometer R
0Direct or indirect and amplifier input end links, and when directly linking, adjusts R
0Can change by A
1And A
2The balance of the overall impedance of the amplifying circuit of forming causes the CMRR of whole prime amplifier to reach more than the 60dB, adjusts potentiometer R
0Resistance, can change the overall symmetrical balance of each direct current resistance, adjust in three elements of circuit potentiometer R
0Span is chosen between 30k～100k Ω, and R
2=R
0, R
12=0.5R
0, the principle that resistance is chosen should guarantee that total direct current input impedance of whole prime amplifier is no more than 500k Ω.
Integrated transporting discharging A in the above-mentioned integrated operational amplifier
1Positive feedback loop in insert by resistor R
3, R
4, R
5With the T-network of capacitor C l composition, wherein R
3, R
4And R
5Respectively there is an end to be associated in together, in their other end, R
4Ground connection, R
3Meet A
1In-phase input end, R
5Meet the output terminal VO of Al
+, integrated transporting discharging A
2Positive feedback loop in insert by resistor R
13, R
14, R
15And capacitor C
2The T-network of forming, wherein R
13, R
14And R
15Respectively there is an end to be associated in together, in their other end, R
14Ground connection, R
13Meet A
2In-phase input end, R
15Meet A
2Output terminal V
O -, ac coupling capacitor C
1And C
2Value is 0.01 μ～0.1 μ F,
T-network is formed amplifier direct current input impedance R
iA part:
R
i＝2(R
1+R
2+R
3+R
4)≤500kΩ (1)
T-network exchanges input impedance with other element composition amplifier:
r
i＝2(R
1+R
2+2πf
0·C
1·R
3·R
4)≥10MΩ (2)
F in the formula
0It is the frequency of operation of ultrasonic probe.r
iValue should design more than 10M Ω, even reach more than the 100M Ω.The output impedance r of ultrasonic probe is looked in the design of this value
0Determine, in the T-network, R
3=R
13, R
4=R
14, (R
3+ R
4)＜200k Ω, R
5=R
15=2k Ω, C
1=C
2, be taken within 0.1 μ～0.01 μ two integrated transporting discharging A according to formula (2)
1And A
2The negative feedback end negative feedback resistor R is respectively arranged
6=R
16=(R
3+ R
4), two negative feedback resistors can guarantee and A
1And A
2The dc balance of in-phase end.
Above-mentioned integrated circuit is a differential input, differential output prime amplifier.With A
1And A
2For two cover amplifying circuits of representative should keep their overall symmetry, this assurance is corresponding identical respectively and realize by two cover electronic components up and down.The resistance Matching Error should be within ± 0.5% scope, and the capacitance pairing error should guarantee in ± 5%, amplifier A
1And A
2Should select for use bandwidth gain to amass double operational in 5M～50MHz scope, this scope is by the decision of probe frequency of ultrasonic.
The gain of prime amplifier is bordering on 1, its output terminal V
O +And V
O -To link with the input end of post-amplifier.Its input end V
i +And V
i -To link with the ultrasonic probe lead-in wire.
Typical case's application technology
The application circuit of adjoint 1,2:
Order probe frequency of operation f0=100kHz.If the interchange input impedance ri of design circuit then makes R greater than 60M Ω
1=R
11=50k Ω, D
1And D
2Use the ordinary silicon diode; Make R
0=R
2=30k Ω, R
12=15k Ω.Make R
3=R
13=75k Ω, R
4=R
14=75k Ω, R
5=R
15=2k Ω, C
1=C
2=0.1 μ F.
Can check direct current input impedance according to formula (1):
Ri＝2(R
1+R
2+R
3+R
4)＝460KΩ
If when not satisfying Ri＜500k Ω, can reduce R in proportion simultaneously
1, R
2, R
3And R
4Resistance, when satisfying till.
Can check interchange input impedance according to formula (2):
Ri=2 (R
1+ R
2+ 2 π f0C
1R
3R
4)=2 (50k+30k+6.28 * 100k * 75k * 75k * 0.1 μ) ≈ 70M Ω can change C simultaneously when ri does not satisfy design objective
1=C
2Value realize.
As seen the about 460k Ω of this amplifier direct current input impedance greatly reduces amplifying circuit and gets the dc shift characteristic.Can reach 70M Ω and exchange input impedance, can be from the ultrasonic voltage signal of probe acquisition more than 99%.
It is MAX4132 that double operational A1 and A2 select model for use.
The method of adjustment of common-mode rejection ratio (CMRR):
With two input end V in the accompanying drawing 1,2
i +And V
i -Insert a 50Hz AC sine signal within 5～10V after the short circuit over the ground, with simulation city's electrical interference.Use oscillograph to observe the V of this sinusoidal input signal and amplifying circuit simultaneously
O +And V
O -Between the 50Hz output signal.Adjust potentiometer R repeatedly
0Can make the amplitude of exporting the 50Hz waveform reach minimum gets final product.
Claims (1)
1. the high input impedance difference preliminary amplifier circuit of a ultrasonic flow meter; it is characterized in that: comprise high tension protection circuit; CMRR adjusts circuit; integrated operational amplifier; described high tension protection circuit: comprise resistance R 1; resistance R 11; diode D1; diode D2; described CMRR adjusts circuit and comprises potentiometer R0; resistance R 2; resistance R 12; described integrated operational amplifier; comprise integrated operational amplifier circuit A1; integrated operational amplifier circuit A2; resistance R 6; resistance R 16; resistance R 3; resistance R 4; resistance R 5; resistance R 13; resistance R 14; resistance R 15; capacitor C 1; capacitor C 2; wherein two resistance R 1 and resistance R 11 and protection diode D1 and diode D2 form the amplitude limiter circuit of series loop form; diode D1; the two ends of diode D2 parallel connected in reverse phase are respectively through resistance R 2; resistance R 12 and integrated operational amplifier circuit A1; the in-phase input end of integrated operational amplifier circuit A2 links; potentiometer R0 directly or indirectly and high tension protection circuit and integrated operational amplifier circuit input end link; adjust the resistance of potentiometer R0; can change the overall symmetrical balance of each direct current resistance; be provided with resistance R 3 in the positive feedback loop of integrated operational amplifier circuit A1; resistance R 4; the T-network that resistance R 5 and capacitor C 1 are formed; wherein resistance R 3; resistance R 4 and resistance R 5 respectively have an end to be associated in together; in their other end; resistance R 4 ground connection; resistance R 3 connects the in-phase input end of integrated operational amplifier circuit A1; resistance R 5 meets the output terminal VO+ of integrated operational amplifier circuit A1 through capacitor C 1; the positive feedback loop of integrated operational amplifier circuit A2 is provided with resistance R 13; resistance R 14; the T-network that resistance R 15 and capacitor C 2 are formed; wherein resistance R 13; resistance R 14 and resistance R 15 respectively have an end to be associated in together; in their other end; resistance R 14 ground connection; resistance R 13 connects the in-phase input end of integrated operational amplifier circuit A2; resistance R 15 meets the output terminal VO one of integrated operational amplifier circuit A2 through capacitor C 2; be arranged on two negative feedback resistor R6 and the resistance R 16 of integrated operational amplifier circuit A1 and integrated operational amplifier circuit A2; gain with the control prime amplifier; the output terminal of resistance R 6 one termination integrated operational amplifier circuit A1 wherein; another termination inverting input; the output terminal of resistance R 16 1 termination integrated operational amplifier circuit A2, another termination inverting input.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2008100527688A CN101251399B (en) | 2008-04-17 | 2008-04-17 | High input impedance differential pre-amplifier circuit of ultrasonic flowmeter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2008100527688A CN101251399B (en) | 2008-04-17 | 2008-04-17 | High input impedance differential pre-amplifier circuit of ultrasonic flowmeter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101251399A CN101251399A (en) | 2008-08-27 |
| CN101251399B true CN101251399B (en) | 2010-06-09 |
Family
ID=39954905
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2008100527688A Expired - Fee Related CN101251399B (en) | 2008-04-17 | 2008-04-17 | High input impedance differential pre-amplifier circuit of ultrasonic flowmeter |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN101251399B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103162751B (en) * | 2013-02-05 | 2015-04-15 | 天津大学 | Ultrasonic flowmeter |
| CN104423388A (en) * | 2013-09-03 | 2015-03-18 | 北京谊安医疗系统股份有限公司 | Control device for anaesthesia machine flow meter |
| TW201624914A (en) * | 2014-12-18 | 2016-07-01 | 力智電子股份有限公司 | Signal amplifying circuit |
| CN110530249B (en) * | 2019-08-30 | 2021-07-06 | 无锡市海鹰工程装备有限公司 | Preamplifier of induction synchronizer and induction synchronizer thereof |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4812780A (en) * | 1986-04-23 | 1989-03-14 | Texas Instruments Incorporated | Broadband differential amplifier |
| CN1619948A (en) * | 2003-11-19 | 2005-05-25 | 三洋电机株式会社 | Amplifier |
-
2008
- 2008-04-17 CN CN2008100527688A patent/CN101251399B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4812780A (en) * | 1986-04-23 | 1989-03-14 | Texas Instruments Incorporated | Broadband differential amplifier |
| CN1619948A (en) * | 2003-11-19 | 2005-05-25 | 三洋电机株式会社 | Amplifier |
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| Publication number | Publication date |
|---|---|
| CN101251399A (en) | 2008-08-27 |
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Granted publication date: 20100609 Termination date: 20180417 |