Calculating Liquid Volume in LOGO! 8 with Pressure Sensors

Good afternoon! You're right to identify the LOGO!'s limitations with very large numbers and floating-point calculations for your application.

Problem Summary

You have 5 cylindrical containers with liquids of varying densities, each equipped with a 4-20mA pressure sensor (0-16000 Pa range). You want to determine the volume (liters) or mass (kg) of liquid in each container using LOGO! 8, but the LOGO!'s math functions struggle with the required calculations.

Solution Approach & Recommendations

The LOGO! 8 is not ideally suited for complex floating-point math. Here's a breakdown of why and potential solutions:

1. The Challenge: Converting pressure to height, then to volume (πr²h), and finally to mass (density * volume) involves floating-point operations and potentially large numbers that exceed the LOGO!'s processing capabilities.
2. Scaling & Approximation: You could attempt to scale down the calculations. However, given the cylinder dimensions (800mm diameter, 800mm height), the pressures involved will likely still result in numbers that are difficult for the LOGO! to handle precisely.
3. External Calculation & Communication (Recommended): The most reliable solution is to offload the complex calculations to an external device (e.g., a PLC, HMI, or PC) and communicate the pressure readings from the LOGO! 8 to that device. The external device can perform the calculations and send the result *back* to the LOGO! 8 for display or control purposes.

Communication Options

• Modbus TCP/IP: LOGO! 8 supports Modbus TCP/IP, allowing it to send pressure readings to a Modbus master (like a PLC or SCADA system). Siemens Support - LOGO! 8 Modbus TCP
• LOGO! Soft Comfort Communication: If using a Siemens HMI, you can establish communication directly with the LOGO! 8.

Simplified Formula & Considerations (If attempting within LOGO! 8)

If you *must* attempt calculations within the LOGO! 8, consider these limitations:

• Pressure to Height: Height (h) = Pressure (Pa) / (Density (kg/m³) * Gravity (9.81 m/s²)). You'll need to know the density of each liquid.
• Volume Calculation: Volume (m³) = π * r² * h (where r = 0.4m). Approximate π as 3.14.
• Scaling: Multiply results by appropriate conversion factors (e.g., 1 m³ = 1000 liters).

Important Disclaimer: Accuracy will be limited due to the LOGO!'s math capabilities. Thorough testing and calibration are crucial.

For further assistance with Modbus configuration or communication protocols, please refer to the Siemens Industry Online Support.