One of the biggest problems when working in the area of industrial instrumentation and sensors is to perform the reading of a sensor signal with the industrial pattern of voltage or current through industrial control equipment.
Most sensors are elements that provide low signals at their output as it is excited according to a measured variable.
And to ensure the reading of this signal with industrial equipment, a signal-matching circuit is required for industrial voltage and/or current reading patterns.
Therefore, in this article, we will explain the procedure to supply a signal from 0V to 10V (industrial standard) using a circuit with an operational amplifier applied in instrumentation.
The Solution - Operational AmplifiersAs already explained, the solution for reading and amplifying the low signal supplied by the sensors is to amplify this signal to ensure an adequate reading by the industrial controllers.
And for this, the need arises for the use of operational amplifiers.
Operational amplifiers are very high gain amplifiers with very high input impedance (in the megaohms range) and a low output impedance with a value of less than 100 ohms.
Among the various configurations of connections of the operational amplifiers, the non - inverting add - on amplifier configuration will be used. This configuration has is represented by the following circuit below:
The equation that relates the output voltage (Vout) to the input voltage values is:
Where:
Vout: Output voltage
Vin: Input voltage
The ProjectTo accomplish this project, we will explain how to perform the transformation of an output signal from a sensor ranging from 0 mV to 1000 mV for a signal in the range of 0V to 10V.
Using the non-inverting adder configuration, we will amplify this signal at the input of a circuit and we will obtain the value 0V for 0 mV of input and the value 10 V for the value of 1000 mV of input.
But for this, we must know the gain value for the amplification of the signal.
To calculate the gain (k), we use the following equation:
Now, based on equation 1, we must calculate the output gain based on the use of resistors using the non-inverting adder configuration.
As it is possible to observe in this equation, to have the value of gain 10, we must choose two values of resistance, to guarantee a value 9 in the division between them. Once added to the value 1, we will have atotal gain of 10.
In the calculation of the design, a resistor of 27kR and 3kR was used. Based on the resistor calculation values, the circuit is shown in Figure 2 with the operational amplifier LM741:
From the circuit shown in Figure 2, we note that when injecting an input signal between 0 mV and 1000 mV, a signal will emerge within the range of 0 V and 10 V.
ApplicationA great utility for this circuit is to apply it to amplify the signal of the LM35D temperature sensor, to transmit its signal in the industrial voltage standard to a programmable logic controller.
The LM35D is a linear sensor, that is, it has an output signal of 10mV /ºC. At 0° C provides an output signal of 0mV and at 100 °C, it provides a 1000mV signal.
Therefore, through the circuit shown in Figure 2, it is possible to transmit its signal in the industrial voltage standard. Below is the circuit with the LM35D sensor in Figure 3.
The Silícios Lab thanks you for reading and following the published content and PCBWay for the support.
The Silícios Lab thanks the UTSOURCE to offer the electronic components for this project.
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