I have a weighing system that needs to be modernized. The system consists of 14 hoppers, each equipped with a load cell that sends a signal to an amplifier with an output signal ranging from 0 to 10 volts. Can a Programmable Logic Controller (PLC) with analog input modules be used to compare the weight in each hopper with a preset value and trigger a solenoid valve to release the material into a packing machine? Are there any time response limitations for the PLC (scan time)? Will this system be accurate and efficient? I look forward to your response.
Most PLC brands are equipped with analog input cards that can accept a 0-10 VDC signal. Through the use of mathematical functions or built-in scaling functions (depending on the brand), this input data can be converted into engineering units. PLCs typically feature ">" and "<" functions for comparing actual weight to a predetermined limit and activating hoppers accordingly. Utilizing a PLC is a reliable solution for this problem unless ultra-fast response time (less than a few milliseconds) is required. It is advisable to reach out to local distributors for assistance in selecting PLC hardware and programming software, allowing them to offer guidance in getting started with the setup.
Thank you for your interest. Each of the 14 hoppers is simultaneously fed from a linear vibrator, which in turn is powered by a main radial vibrator. This setup allows for a continuous weighing process for all 14 hoppers at once. The system compares the combined weight of the hoppers to a pre-set value and only opens one hopper accordingly. There is a concern that the PLC may struggle to update the readings from all 14 channels simultaneously, potentially causing a delay in the opening and closing signals for the hoppers. This delay, attributed to scan time, could result in the weight being slightly higher than the desired setting, leading to inaccuracies.
I am not completely certain about the specific issue you are facing, but a Programmable Logic Controller (PLC) can address issues such as scan time, material-in-flight, and valve closing time through the use of a pre-act feature. Rather than stopping the process once the setpoint is reached, the process stops when the setpoint minus the pre-act value is achieved. By carefully adjusting the pre-act setting, the desired amount of material can be transferred effectively. Additionally, a system can be set up to automatically adjust the pre-act value based on the process performance, reducing undershoots and overshoots. If precision is crucial, using a PLC is essential. How do you plan to achieve the same level of accuracy without incorporating a PLC?
When it comes to accuracy in systems, it's important to not just focus on PLC scan time, but also consider the resolution and update time of analog input modules. Generally, higher resolution in analog modules means less frequent updates for each channel. It's crucial to review the data sheets of the modules you are considering, as some channels may not be updated as frequently as once per I/O scan. A key factor to consider is how often fresh load cell data can be expected to be received by the PLC. This, combined with the fill rate of hoppers, will determine if weight variation falls within an acceptable tolerance range. For example, if hoppers are filling at 100 grams per second and the PLC is receiving load cell updates every 50 milliseconds, increments of 5 grams will be used. Additionally, it's essential to choose the right size of load cell for the application to ensure accurate measurements. Avoid using a 1000 Kg load cell to measure a 10 Kg load to prevent inaccuracies.
Many leading PLC brands provide specialized weighing modules, which can directly connect with load cells and offer high-speed outputs. These modules handle weighing calculations and outputs autonomously, without being affected by processor scan time. For more details on Schneider Electric's weighing module options, visit their website at http://www.schneiderautomation.com/Default.htm.
Using a Programmable Logic Controller (PLC) with analog input modules would indeed allow you to compare the weight in each hopper to a preset value and activate a solenoid valve accordingly. In terms of accuracy, a well-programmed PLC should provide reliable and dependable responses. As for scan time or time response, it largely depends on the specific model and brand of the PLC, along with your programming. In a general sense, PLCs are able to handle complex tasks efficiently and can usually execute a routine within a few milliseconds. The real challenge lies in the profiling and commissioning of the PLC to ensure seamless interaction with your weighing system, and it might be worthwhile to involve a professional specializing in automation and control systems for this.
Absolutely, a PLC with analog input modules can efficiently handle this application. Its scan time, which measures its speed in performing all program functions, is usually fast enough for most processes, unless the application is highly time-sensitive. As for accuracy, this would depend on the resolution of your analog input module and the quality of your load cell. But barring any significant noise or interference in the signal, you should find both the accuracy and efficiency to be satisfactory. It's crucial to select the right PLC and program it correctly. Do remember to continually calibrate and maintain your load cells for best results.
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Answer: - Yes, a PLC with analog input modules can be used to compare the weight in each hopper with a preset value and trigger a solenoid valve for material release.
Answer: - The time response or scan time of the PLC will depend on the specific model and programming complexity, but it should be fast enough for real-time control in weighing applications.
Answer: - When properly configured and calibrated, the PLC-based system should provide accurate and efficient control of material flow based on the weight measurements from the hoppers.
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