Circuit Design and Examples. Design Guidelines Objectives Sensor Signal Conditioning Example Instrumentation Amplifiers AD620 OpAmps Op07 (modern) LM741 (ancient). Design Guidelines-1. Define the measurement objective
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Sensor Definition in Engineering: the component of an instrument that converts
an input signal into a quantity that is measured by another part of the instrument
and changed into a useful signal for an information-gathering system.Design Guidelines-2
A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
2.33: A bridge circuit has R1=R2=R3=120 ohms and V=10.0 volts. Design a signal conditioning system that provides an output of 0 to 5 volts as R4 varies from 120 to 140 ohms. Plot Vout vs R4. Evaluate the linearity
Desired output is VA-B
0 to .3846 to 0 to 5
Requires a gain of
Analog Devices Inc. is the largest supplier of instrumentation amplifiers in the world.
The AD620 is a low cost, high accuracy instrumentation amplifier which requires only one external resistor to set gains of 1 to 1000. Furthermore, the AD620 offers lower power (only 1.3 mA max supply current), making it a good fit for battery powered, portable (or remote) applications.
The AD620, with its high accuracy of 40 ppm maximum nonlinearity, low offset voltage of 50 µV max and offset drift of 0.6 µV/°C max, is ideal for use in precision data acquisition systems, such as weigh scales and transducer interfaces. The low noise, low input bias current, and low power of the AD620 also make it well suited for medical applications such as ECG and noninvasive blood pressure monitors.
The low input bias current of 1.0 nA max is made possible with the use of Superbeta processing in the input stage. The AD620 works well as a preamplifier due to its low input voltage noise of 9 nV/Hz at 1 kHz, 0.28 µV p-p in the 0.1 Hz to 10 Hz band, 0.1 pA/µHz input current noise. The AD620 is also well suited for multiplexed applications with its settling time of 15 µs to 0.01% and its cost is low enough to enable designs with one in amp per channel.
common-mode rejection ratio (CMRR): The ratio of the common-mode interference voltage at the input of a circuit, to the corresponding interference voltage at the output.
Make vs. Buy: A Typical Bridge Application Error Budget instrument that converts
The AD620 offers improved performance over “homebrew” three op amp IA designs, along with smaller size, fewer components and lower supply current. In the typical application, a gain of 100 is required to amplify a bridge output of 20 mV full scale over the industrial temperature range of –40°C to +85°C.
Regardless of the system in which it is being used, the AD620 provides greater accuracy, and at low power and price.
Note that for the homebrew circuit, the OP07 specifications for input voltage offset and noise have been multiplied by 2, because a three op amp type in-amp has two op amps at its inputs.AD620 vs opamp
The LM741 series are general purpose operational amplifiers which feature improved performance over industry standards like the LM709. They are direct, plug-in replacements for the 709C, LM201, MC1439 and 748 in most applications.
$1.25 for one Op07
25 for $25
$0.44 for one LM741
25 for $8
Boolean Algebra Example
Comparators and Circuits
Generalized AC Bridge
Z1Zx = Z2Z3
Condition for Balanced Bridge
Expected Sine Wave
Adjust the 50K resistor
for a sine wave output
BITSA bit is the smallest element of information used by a computer. A bit holds ONE of TWO possible values: 0 meaning Off/False/NotSet and 1 meaning On/True/Set
Boolean algebra recognizes True and False. So a single bit can represent a Boolean variable.
NIBBLEA nibble is a group of FOUR bits. This gives a maximum number of 16 possible different values. 2 ^ 4 = 16
LSB and MSB:The Least Significant Bit (LSB) is always drawn at the extreme right and has the least value and the Most Significant Bit (MSB) is always shown on the extreme left, and is the bit with the greatest value.
BYTESBytes are a grouping of 8 bits. This comprises TWO nibbles.
Binary Coded Decimal [BCD]Binary code decimal digits (0-9) are represented using FOUR bits. The valid combinations of bits and their respective values are 0000 through 1001 with the binary combinations 1010 to 1111 not used.
If the computer stores one BCD digit per byte, its called normal BCD. The unused nibble may be all 0's or all 1's.
If two BCD digits are stored per byte, its called Packed BCD. This occurs in data transmission where numbers are being transmitted over a communications link. Packed BCD reduces the amount of time spent transmitting the numbers, as each data byte transmitted results in the sending of two BCD digits.
Refers to the base-16 number system, which consists of 16 unique symbols: the numbers 0 to 9 and the letters A to F. e.g. decimal 15 is represented as F in hexadecimal. This is useful because it can represent a byte (8 bits) as two hexadecimal digits. It is easier to read hexadecimal numbers than binary numbers.
To convert a value from hexadecimal to binary, translate each hexadecimal digit into its 4-bit binary equivalent. Hexadecimal numbers have either an 0x prefix or an h suffix. For example, the hexadecimal number 0x3F7A translates to the following binary number: 0011 1111 0111 1010
24 volt dc
A + B
C + D
Open-drain outputs are outputs which at any given time are either actively sinking current (i.e., low voltage, typically considered logic 0) or are high impedance, but which never source current (high voltage, logic 1). Open-drain refers to the drain terminal of a MOS FET transistor. The equivalent concept on a bipolar device is called open-collector.
Article on the meaning of Rail-to-rail
LM339 is $0.52 at Digikey
100 Hz Sinusoid