Download Instrumentasi Elektronika (Electronic Instrumentation)

Instrumentasi Elektronika
(Electronic Instrumentation)
BAB 3
SIGNAL CONDITIONING & CONVERSION
CAPAIAN PEMBELAJARAN
Setelah mengikuti kuliah ini mahasiswa mampu:
1
Menjelaskan fungsi pengkondisi sinyal analog
2
Mendesain rangkaian RC low-pass dan high pass filter untuk
menghilangkan sinyal yang tidak diinginkan.
3
Mendesain rangkain jembatan Wheatstone untuk mengkonversi
perubahan tegangan terhadap perubahan resistansi
4
Menjelaskan fungsi Op-amp sebagai pengkondisi sinyal
5
Menjelaskan cara kerja sebuah penguat instrumentasi
6
Mendesain sistem pengkondisi sinyal analog untuk mengkonversi
berbagai masukan tegangan untuk beberapa rentang output yang
diinginkan
7
Merancang pengkondisi sinyal analog untuk berbagai variasi input
resistansi diubah menjadi berbagai variasi tegangan yang
diinginkan.
POKOK BAHASAN
Rangkaian
RLC (Filter
LPF dan
HPF)
Penguat
Instrumentasi
Pengkondisi
Sinyal
Operational
Amplifier
(Op-Amp)
Rangkaian
Pembagi
dan
Jembatan
SISTEM AKUISISI DATA
Pengkondisi Sinyal
4
RANGKAIAN INTERFACE
Antarmuka atau sirkuit pengkondisi sinyal berfungsi membawa
sinyal dari sensor sampai ke beban dengan format yang kompatibel
SISTEM INSTRUMENTASI PADA KENDARAAN
FUNGSI PENGKONDISI SINYAL
1. Linierisasi
5.
Conversion
Fyngsi
Pengkondisi
sinyal
4. Filtering
dan Matching
Impedance
2. Perubahan
bias dan level
sinyal
3. Efek
Pembebanan
1. Linierisasi
Tujuan linierisasi adalah
untuk memberikan output
yang bervariasi secara linear
terhadap beberapa variabel
termasuk jika output
sensornya tidak linier.
2. Signal Level and Bias Changes
Signal Level and Bias Changes berfungsi
menyesuaikan tingkat (besarnya) dan bias (nilai
nol) dari beberapa tegangan yang mewakili
variabel proses.
Standar sinyal dalam instrumentasi
• Tegangan 0V – 10V, atau 0V -5V
• Arus 4 – 20 mA
• Tekanan 3 – 15 psi

Output sensor 0,2V – 0,6V,
peralatan pemroses memerlukan
tegangan bervariasi 0V – 5V.

Output sensor 0V – 24V,
peralatan pemroses memerlukan
tegangan 0V – 5V
Bagaimana
solusinya:
3. Efek Pembebanan (lanjutan)
Kita perlu mengetahui drop
tegangan pada beban
dengan label Vy. Melalui
hukum Ohm tegangan Vy
dapat diketahui dengan
mengurangkan Vx dengan
arus dikalikan Rx.
Vy = Vx – I.Rx
3. Efek Pembebanan (lanjutan)
Example: An amplifier
outputs a voltage that is
10 times the voltage on
its input terminal. It has
an input resistance of 10
kΩ. A sensor outputs a
voltage proportional to
temperature with a
transfer function of
20mV/ °C. The sensor has
an output resistance of
5.0 kΩ. If the
temperature is 50 °C, find
the amplifier output.
Figure 2.3
3. Efek Pembebanan (lanjutan)
4. Filtering dan Matcing Impedansi
• Filtering adalah mengeliminasi sinyal yang
tidak diinginkan dalam loop proses kontrol
(Instrumentasi)
• Impedance matching adalah impedansi
internal tranduser atau impedansi line yang
dapat menyebakan error dalam pengukuran
variabel dinamis.
5. Conversion
• Convert one type of electrical variation into
another.
• Signal Transmission (Voltage to current,
Current to Voltage converter)
• Digital Interface (ADC requires 0-5V input)
Standar sinyal dalam instrumentasi
• Tegangan 0V – 10V, atau 0V -5V
• Arus 4 – 20 mA
• Tekanan 3 – 15 psi
Rangkaian RLC,
Filter LPF dan HPF
RANGKAIAN RC
Jawab:
Berapa tegangan pada kapasitor setelah 35
uS inputnya diberikan input step dari 0 ke
54V, jika R = 47k-ohm dan C = 1,5uF
Time Constant pada Rangkaian RC
Rangkaian RC dengana input step, maka tegangan pada
kapasitor adalah:
Ec = E (1− e−t/ RC)
Tegangan keti pengosongan kapasitor:
Ec = E . e−t /RC
Berapakah time constant untuk rangkain RC di atas jika R= 220 kohm dan C = 2,2 uF.
RANGKAIAN RL
RANGKAIAN RCL
TEGANGAN DALAM RANGKAIAN RCL
XC = XL
Berapa arus yang mengalir pada rangkaian
RCL jika R=27k-ohm, C = 2,2nF, L=33mH,
dan E = 20V dengan frekuensi 35 k-Hz
RANGKAIAN RCL
(lanjutan..1)
FREKUENSI RESONANSI
Merupakan frekuensi yang
menyebabkan arus pada rangkaian
RLC maksimum. Hal tersebut bisa
dicapai ketika XL = XC.
Rangkaian RLC seri
Rangkaian RLC paralel
FILTER RC
Jenis-jenis Filter RC:
• High-pass. Meneruskan frekuensi tinggi dan menahan
frekuensi rendah;
• Low-pass. Meneruskan frekuensi rendah menahan
frekuensi tinggi;
• Band-pass. Menersukan frekuensi dengan range tertentu;
• Band reject. Menahan range frekuensi tertentu;
• Twin – T. Filter Band Reject, tetapi dengan karakteristik
respon yng lebih sempit/tajam.
To eliminate unwanted noise signals from measurements, it
is often necessary to use circuits that block certain
frequencies or bands of frequencies.
LOW PASS FILTER (LPF)
First order and second
order low-pass filters,
Gain vs frequency characteristics
of first order and second order filters.
Designing the anti-aliasing filter
• Note
ω is in radians
ω = 2πf
• Exercise: Find an R+C pair so that the half-power
point occurs at 30 Hz
FILTER RC
Highh Pass
High
(a) High-pass filters, (b) band-pass filters, (c) twin-T band reject filters, and (d)
their frequency characteristics.
FIGURE 2.16. Response of the high-pass RC filter
as a function of frequency ratio.
Rangkaian Pembagi Tegangan
dan Jembatan
RANGKAIAN PEMBAGI TEGANGAN
Figure 2.4
30
31
EKT314/4 - Electronic Instrumentation
32
RANGKAIAN JEMBATAN DC
Bridge circuits are used to convert
impedance variations into voltage
variations
Figure 2.5
RANGKAIAN JEMBATAN DC (lanjutan)
if
Zero difference and zero voltage
across the detector
EKT314/4 - Electronic Instrumentation
35
*-ve result means that Vb larger Va.
EKT314/4 - Electronic Instrumentation
36
FIGURE 2.6
When a galvanometer is used for a null detector, it is convenient to use the
Thévenin equivalent circuit of the bridge.
EKT314/4 - Electronic Instrumentation
38
Bridge resolution:
A function of the resolution of the
detector used to determine the
bridge offset.
39
40
FIGURE 2.7
For remote sensor applications, this compensation system is used to avoid errors from lead resistance.
LEAD COMPENSATION
-When bridge circuit may be
located at considerable
distance from the sensor
whose resistance changes
are to be measured.
-Problem many effect that
change the resistance.
-any changes in lead
resistance are introduced
equally into both arms of the
bridge circuit, thus causing
no effective change in bridge
offset
FIGURE 2.8
The current balance bridge.
CURRENT BALANCE BRIDGE
-this method uses a current to null
the bridge
Figure. 2.8
EKT314/4 - Electronic Instrumentation
43
Potential measurement using bridges:
A bridge circuit is useful for measuring small
potentials at very high impedance using either a
Wheatstone bridge or current balance bridge.
Performs by placing the potential to be
measured in series with the detector.
44
FIGURE 2.9
Using the basic Wheatstone bridge for potential measurement.
Using Wheatstone bridge
Using Current balance bridge
46
47
ac bridges
48
ac bridges
FIGURE 2.10
A general ac bridge circuit.
FIGURE 2.11
The ac bridge circuit and components for Example 2.10.
51
FIGURE 2.12 (a) Bridge off-null voltage is clearly nonlinear for large-scale changes in resistance. (b) However, for small ranges of
resistance change, the off-null voltage is nearly linear.
Primary application of bridge circuits
-To Convert variations of resistance into
Variations of voltage
If the range of resistance variation is
Small and centered about the null value Then
then nonlinearity of voltage Resistance is
small.
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Rangkaian Operational Amplifier
(Op-Amp)
∆Vin = V1-V2
-∆Vin = V1-V2
KONFIGURASI OP-AMP
Voltage
follower
Differensial
Amplifier
Inverting
Amplifier
Op-Amp
Summing
Amplifier
NonInverting
Amplifier
The op amp voltage follower. This circuit has unity gain but
very high input impedance.
High impedance
Low impedance
The op amp inverting amplifier.
FIGURE 2.27 (continued)
Nonideal characteristics of an op amp include finite gain, finite impedance, and offsets.
FIGURE 2.28
Some op amps provide connections for an input offset compensation trimmer resistor.
FIGURE 2.29
Input offset can also be compensated using external connections and trimmer resistors.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
A noninverting amplifier.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
The op amp summing amplifier.
The basic differential amplifier configuration.
An instrumentation amplifier includes voltage followers for
input isolation.
PENGUAT INSTRUMENTASI
67
FIGURE 2.39
A voltage-to-current converter using an op amp.
69
EKT314/4 - Electronic Instrumentation
70
FIGURE 2.40 A current-to-voltage converter using an op amp. Care must be taken that the current output capability of the op amp is
not exceeded.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 2.41
An integrator circuit using an op amp.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 2.42
This circuit takes the time derivative of the input voltage.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
FIGURE 2.43
A nonlinear amplifier uses a nonlinear feedback element.
Curtis Johnson
Process Control Instrumentation Technology, 8e]
Copyright ©2006 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.