In industrial automation and control applications where various measurement units are used for various processes, PLCs are frequently used. PLC programming must take into account the units of measurement used in the process to ensure accurate and reliable control. Unit conversion in PLC programming becomes crucial at this point.
In Rockwell Automation PLC programming, unit conversion entails converting a value measured in one unit of measurement to another that is more appropriate for a given process. Usually, scaling factors or conversion equations are used for this.
Here are some important factors to take into account when using unit conversion in PLC programming:
1. Determine the units of measurement used in the process:
It’s crucial to understand the units of measurement used in the process before programming the PLC. The values here could be in degrees Celsius or Fahrenheit, PSI or bar pressure, or liters per minute or gallons per minute flow rate.
The units of measurement used in a process must be identified prior to programming a PLC for that process. To translate raw sensor readings into useful units that can be applied to process control, this information is required.
For instance, the units of measurement used in a temperature control process could be Celsius, Fahrenheit, or Kelvin. The units of measurement used in a pressure control process could be PSI, bar, or Pascal. Similar to this, liters per minute, gallons per minute, or cubic meters per hour could be the units of measurement in a flow control process.
It’s important to remember that various regions and industries might use various measurement systems for the same process. Determining the measurement units used in the particular process under control is crucial. Diagrams of the process, instruction books, or consultations with subject matter experts in the area can all provide this information.
Following the identification of the units of measurement, a PLC program can be created to transform raw sensor readings into useful units for process control. Scaling factors, conversion equations, or a combination of the two may be used in this situation. Making sure the PLC is programmed to correctly interpret and react to sensor readings in the appropriate measurement units for the process being controlled is the main objective.
2. Calculate the scaling factor:
A sensor’s raw value is transformed into a useful unit using the scaling factor. Based on the sensor’s resolution, full-scale range, and desired unit of measurement, the scaling factor is determined. The scaling factor, which is used to translate the raw sensor value into degrees Celsius, might be 0.1 in the case of a temperature sensor with a full-scale range of 0-100°C and a resolution of 0.1°C.
The scaling factor is a conversion factor used to convert a raw sensor reading into a meaningful unit of measurement in a PLC program. It is calculated based on the full-scale range of the sensor, the resolution of the sensor, and the desired unit of measurement.
The sensor’s measurement range, from the smallest to the largest value, is known as its full-scale range. For instance, the full-scale range of a temperature sensor with a full-scale range of 0-100°C is 100 – 0 = 100.
3. Use conversion equations:
Sometimes, unit conversion in Allen Bradley 1766-L32BXBA MicroLogix 1400 PLC programming requires more than just scaling factors. In these cases, conversion equations can be used to convert from one unit of measurement to another. For example, to convert temperature from Celsius to Fahrenheit, the equation (°F = °C x 1.8 + 32) can be used in the PLC program.
To change a value’s unit of measurement, conversion equations are used in PLC programming. This is frequently required when sensors or equipment produce values in units other than the one desired for the process being controlled.
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4. Testing and calibration:
After the PLC program has been developed, it’s important to test and calibrate the system to ensure that the unit conversion is accurate. This involves comparing the PLC readings to manual readings taken using calibrated equipment.
Testing and calibration are critical steps in ensuring the accuracy and reliability of a PLC system. These steps involve verifying that the inputs and outputs of the PLC system are functioning correctly and that the system is responding appropriately to changes in the process being controlled. In summary, unit conversion in PLC programming is an important aspect of industrial automation and control. It involves converting raw sensor readings into meaningful units using scaling factors and conversion equations. Accurate unit conversion is essential for reliable and effective process control.
