![]() ![]() In fact NXP recommends some kind of zero routine for it: that would zero the opamp offset too.Īs for the gain error: you have 1.5%-2.5% from the transducer, substantially nothing from the opamp and some % from the vref generator. In this case the opamp offset is negligible. However notice how big is the transducer offset tolerance in comparison to the other sources of error: 150mV against some mV of opamp offset. Looking at the values you could conceivably add them up and devise some mean error or maximum error. In any case something like 1% of vref error is plausible too. I have no idea if you are converting from VCC, from an internal VRef (most probably) or from an external vref chip. The ADC has errors too the Vref generator has, mostly, since the ADC core itself is digital (usually!). The opamp has its own offset error (3 to 7mV) since we use it as a voltage follower gain error is negligible (otherwise resistor tolerance will enter into play) At this point each stage will introduce an error both in error and in offset (at a first approximation), and some calculation is needed to reach a verdict.įor example, the NXP sensor has a ☑50mV offset from the nominal 0.6V at 0 bar also there is a (transduction) gain error of up to ☒.5% (depending on the range you use) You have an input in (typically) Pascals and an output in volts. This is a complex issue and deserve a whole book to be explained. At the output side the situation is mostly the same (5mV to Vcc-1.5V, typically), so it will work, too.Īccuracy you require. The LM324 has a CM range from 0 to Vcc-2V so it would need to be powered from at least 5V to cover the whole range. The example sensor, by datasheet, can output from 0.6 to 3V when powered at 3.3V. Signal range, and expecially how much to the rail will it go: that establish the required input common mode range for the amplifier and the output range too. However with more than 10 megaohm of amplifier impedance that doesn't really matter (it would if you didn't buffer it!) Output impedance that's easy, it's specified in the datasheet and says how much can you load it (also the main reason for buffering with a voltage follower) NXP in fact doesn't give it but gives a recommended filter cap and a bandwidth so you could calculate that. With sensors, in general, you'll have to cope with different things: You maybe have a 5V output powered one but the general process is the same. As an example I'll work with an MP3V5004DP since it's the one I use and know. Given the schematic you propose it's not a bridge cell but most probably a voltage output precompensated one. Now, you didn't say which kind of pressure sensor you are interfacing with. The atmega internal ADC is, well, junk like most of the embedded ADCs so the idea is double good. We will do our best to accommodate you.Buffering an ADC input is always a good thing, since they don't handle well source impedence of more than 1k (ADC specs vary, however). If you do not see the part, or quantity of the part, you are looking for, please, let us know. Friendly Note: Be mindful of the many, inexpensive, counterfeits available on the market. ![]() New and Authentic Component(s) - LM324 Quadruple Operational Amplifier ICs.Open-Loop Differential Voltage Amplification:.Differential Input Voltage Range Equal to Maximum-Rated Supply Voltage:.Common-Mode Input Voltage Range Includes Ground, Allowing Direct Sensing Near Ground.Low Supply-Current Drain Independent of.The low supply-current drain is independent of the magnitude of the supply voltage.Īpplications include transducer amplifiers, DC amplification blocks, and all the conventional operational-amplifier circuits that now can be more easily implemented in single-supply-voltage systems. Operation from split supplies also is possible if the difference between the two supplies is 3 V to 32 V, and VCC is at least 1.5 V more positive than the input common-mode voltage. These devices consist of four independent high-gain frequency-compensated operational amplifiers that are designed specifically to operate from a single supply over a wide range of voltages. ![]()
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