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It's just a non-inverting amplifier, the mV range has a gain of about x10, and reads from zero to positive. The pH range has a variable gain, and the reference control allows you to set the reference point at other than zero, so it can read above and below the reference point which presumably would be set to 7?.
You might want to add a 1k 1/4 watt resistor from +12V to GND. The 7812 requires a minimum load of 5ma (I seem to recall that some brands require 10ma min.) to guarantee regulation. The TL081 only draws 1.8ma typically.
You might want to add a 1k 1/4 watt resistor from +12V to GND. The 7812 requires a minimum load of 5ma (I seem to recall that some brands require 10ma min.) to guarantee regulation.
Perhaps you are thinking about the LM317 variable rgulator.
The 78xx fixed regulators have their operating current from input to ground. Only an extremely small leakage current appears at their output.
But they are spec'd and tested with a minimum output cuttent of 5mA when cold.
The LM317 has a max operating current of 10mA which is applied to its output, in order to keep the regulated voltage at its ADJ terminal with a very low current.
The LM117 has a max operating current of 5mA.
The variable regulators need a certain minimum value of their voltage-determining resistors (to sink the operating current) to keep the output voltage from rising without a load.
The 78xx fixed regulators have their operating current from input to ground. Only an extremely small leakage current appears at their output.
But they are spec'd and tested with a minimum output cuttent of 5mA when cold.
The LM317 has a max operating current of 10mA which is applied to its output, in order to keep the regulated voltage at its ADJ terminal with a very low current.
The LM117 has a max operating current of 5mA.
The variable regulators need a certain minimum value of their voltage-determining resistors (to sink the operating current) to keep the output voltage from rising without a load.
The LM317 has a max operating current of 10mA which is applied to its output, in order to keep the regulated voltage at its ADJ terminal with a very low current.
The LM117 has a max operating current of 5mA.
mV output has a fixed amplification range, but using the circuit as a transmitter for a pH sensor, you can set the zero and span, and calibrate it against basic and acid solutions...more than an amplifier, it's a transmitter (intrumentation language)
and i dont know if this circuit would work for a redox sensor.
An instrument capable of detecting the kind of non-equilibrium concentrations of reduced iron and manganese, along with the oxides of nitrogen and sulfur, which are strongly indicative of life processes on Earth. Miniature redox sensors have recently been developed that are capable of withstanding high pressure liquid environments. It is thought that arrays of such sensors could form part of the instrumentation on a probe to search for life in Lake Vostok and, eventually, in oceans that might exist on Jupiter's moons Europa and Callisto.
A pH meter is a specific type of voltmeter with a very high impedance of the input channels. The high impedance is a necessary part of the equipment because of high resistance of the pH glass electrode typically used with pH meters (usually between 20 and 100 MΩ).
The common pH meter has several inputs: for indicator (ion-sensitive or redox) and reference electrodes and temperature sensors such as thermoresistors or thermocouples. Cheaper models require external temperature measurements entered using knob or keyboard.
The pH scale of the device should be calibrated by at least two buffer solutions. Usually one of the buffers used for calibration has pH 7.00 and the second is selected depending on the range where the measurements are to be taken - 10.00 for basic solutions and 4.01 for acidic solutions. This correlates the measured potential of the indicator electrode with the pH scale.
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about redox meters, i've used them in wine fermentation process and effluent tratment process
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