Let us look at the details of Current to Voltage conversion technique used for measuring the sensor outputs.
If you have worked on a circuit design which requires reading a current input like for example an analog 4-20mA sensor, you must have explored several options. One of the commonly used method is drawing the desired current and then convert into voltage with a resistor. The resistor selection here is critical. The voltage developed across this resistor cannot be applied directly to an ADC or an internal ADC of microcontroller. It has to be amplified usign an op-amplifier configuration and then to be conencted to preeceding circuitry. This technique even though looks simple and cost effective does not hold good always as, voltage cannot be used directly to drive other parts of a system without potentially disturbing or altering the voltage. Impedance is inserted into the measuring line that causes an error, amplifier offset voltage is also amplified with a loss of accuracy.
Designers these days are exploring different options to avoid the errors caused during the signal conditioning. The major goal of the designer is to have a precise I-to-V conversion. The other way of measuring current using opamp is to feed input current directly into the summing node and the amplifier output voltage changes to extract the same current from the Summing node through R. Resultant Output Voltage would be VOUT = -IINR as current is flowing into the virtual ground. Output voltage would be positive for currents flowing away from virtual ground. The applications of these circuits are in photomultiplier tubes, accelerometers, photo detectors. This kind of opamp configuration for I to V converters are known as Trans Impedance Amplifiers.
Op-Amp Characteristics which are to be considered during the selection for using in I-to-V conversion:
1. Offset voltage
2. Drift voltage
3. Gain-Bandwidth Product
4. Less Low Frequency Noise (1/f noise)
5. Operating Temperature
If you are a hard core Analog engineer, you would be more interested to use discrete circuitry but most of the engineers across the world would be looking for solutions like OPA380.
At the beginning, before talking about 4-20mA sensor input, an engineer should have got a query regarding the input, why it is current and not voltage? Why 4-20mA and not voltag instead? Why designers have to struggle to convert?
For the electronic devices producing an output and which must be read to sense the things, “linearity” is critical. This helps easy sensing and simple algorithms at the controller end. For some of the devices like photo detectors, current output is very linear over the device operating range.
If you have worked on a circuit design which requires reading a current input like for example an analog 4-20mA sensor, you must have explored several options. One of the commonly used method is drawing the desired current and then convert into voltage with a resistor. The resistor selection here is critical. The voltage developed across this resistor cannot be applied directly to an ADC or an internal ADC of microcontroller. It has to be amplified usign an op-amplifier configuration and then to be conencted to preeceding circuitry. This technique even though looks simple and cost effective does not hold good always as, voltage cannot be used directly to drive other parts of a system without potentially disturbing or altering the voltage. Impedance is inserted into the measuring line that causes an error, amplifier offset voltage is also amplified with a loss of accuracy.
Designers these days are exploring different options to avoid the errors caused during the signal conditioning. The major goal of the designer is to have a precise I-to-V conversion. The other way of measuring current using opamp is to feed input current directly into the summing node and the amplifier output voltage changes to extract the same current from the Summing node through R. Resultant Output Voltage would be VOUT = -IINR as current is flowing into the virtual ground. Output voltage would be positive for currents flowing away from virtual ground. The applications of these circuits are in photomultiplier tubes, accelerometers, photo detectors. This kind of opamp configuration for I to V converters are known as Trans Impedance Amplifiers.
Op-Amp Characteristics which are to be considered during the selection for using in I-to-V conversion:
1. Offset voltage
2. Drift voltage
3. Gain-Bandwidth Product
4. Less Low Frequency Noise (1/f noise)
5. Operating Temperature
If you are a hard core Analog engineer, you would be more interested to use discrete circuitry but most of the engineers across the world would be looking for solutions like OPA380.
At the beginning, before talking about 4-20mA sensor input, an engineer should have got a query regarding the input, why it is current and not voltage? Why 4-20mA and not voltag instead? Why designers have to struggle to convert?
For the electronic devices producing an output and which must be read to sense the things, “linearity” is critical. This helps easy sensing and simple algorithms at the controller end. For some of the devices like photo detectors, current output is very linear over the device operating range.
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