Analog and digital
An analog signal is a physical quantity, which, within a given range, can adopt any value - any continuous intermediate value. The opposite of analog is digital. A digital signal knows just two states: 0 and 1 or “off” and “on”.
From electrical signal to analog value
Basic order of events
Several steps are required for LOGO! to process physical quantities:
LOGO! can read in electric voltages from 0 V to 10 V or electric currents from 0 mA to 20 mA to one analog input.
The physical quantities (e.g. temperature, pressure, speed etc.) must therefore be converted into one electric quantity. This conversion is performed by an external sensor.
LOGO! reads in the electric quantity and, with further processing, this is converted into a standardized value within the range 0 to 1000. This value is then applied in the circuit program on the input of an analog special function.
In order to adapt the standardized value to the application, LOGO! uses an analog special function, while taking into consideration the gain and offset, to calculate the analog value. The analog value is then evaluated by the special function (e.g. analog amplifier). If an analog special function has an analog output, then the analog value is also applied to the output of the special function.
With the LOGO! you can also convert analog values back into an electric voltage. In doing so, the voltage can adopt values between 0 and 10 V.
Using this voltage, LOGO! can control an external actuator, which converts the voltage and also the analog value back into a physical quantity.
The following diagram illustrates this order of events.
Gain
The standardized value is multiplied with a parameter. Using this parameter you can more or less boost the electric quantity. Hence, this parameter is called the “gain”.
Zero point offset
You can add or subtract a parameter to or from the boosted standardized value.
Using this parameter you can more or loss move the zero point of the electric quantity. Hence, this parameter is called the “zero point offset”.
Gain and offset
The analog value is therefore calculated as follows:
Analog value = (standardized value x gain) + offset
The following diagram illustrates this formula and the significance of gain and offset:
The straight line in the graphic describes which standardized value is being converted into which analog value. Gain corresponds to the slope of the straight line and offset to the movement of the zero passage of the straight line on the y-axis.
Analog output
If you connect a special function (that has an analog output) to a real analog output, then note that the analog output can only process values from 0 to 1000.
Possibile settings with LOGO!Soft Comfort
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