Hello Members, Currently, I am working on measuring the speed of a Motor Generator using a proximity sensor. I am exploring the possibility of integrating the speed measurement system without utilizing a High Speed counter module. The generator's specifications indicate a maximum rotation of 250 RPM, with a max potential of 300 RPM. Assuming the maximum RPM, the motor rotates 5 times in one second. I am considering using the Mitsubishi Input Card QX40, which allows for response times to be set at 1ms, 5ms, 10ms, or 20ms. If I set the response time to 1ms (equivalent to a response frequency of 1kHz), would it be feasible to measure the speed of the motor generator using the proximity sensor and the QX40 input card? My configuration includes: 1) QX40 set at 1ms response time, 2) Proximity Sensor (Inductive) detecting a distance of 5mm, and 3) Motor Generator with specs of 250rpm (maximum 300rpm). Can the speed of the motor generator be accurately measured with this setup?
NDT engineers use a laser and reflective tape to measure the speed of a shaft. They can either count the number of pulses within a set timeframe or calculate the time interval between pulses to determine the shaft's velocity. This method is commonly employed in non-destructive testing to assess the performance of rotating machinery.
When considering input module response time, it's important to also factor in PLC scan time, I/O scanning updates, prox switch turn on/off times, and target duty cycles. A 50% duty cycle on the input signal is generally ideal - half on, half off. The PLC class outline on corsairhmi.com introduces the '2-5-10' rule, referencing analog and timing resolutions. It suggests that 2x is the minimum, 5x is good, and 10x is ideal. Calculate the worst case delays in the measurement system to ensure the PLC can meet double the required speed. Accuracy and frequency of speed measurements are crucial considerations, with time between pulses offering quick updates but less steady signals, and pulses per time providing steadier signals with slower updates. A combination solution may involve counting pulses for a minimum time period. It's important to thoroughly research and experiment before implementing additions to the code and HMI communications, as these can impact system performance. Ultimately, it's essential to determine the level of accuracy needed for speed measurement and update frequency. While your proposed solution shows promise, additional research and testing are necessary. Avoid overcomplicating things if rocket science isn't required for your specific application.
A more efficient solution would be to utilize a Digital to Analog converter like the Wago 857-500 to set up a scale with parameters for a 4-20ma analog input. Adjusting the scale may be necessary to ensure precision. This method appears simpler than attempting to modify the overhead system.
Calculating RPM involves a straightforward formula: (K x N) / ΔT, where K is the time ticks per minute, N is the number of pulses, and ΔT is the time ticks to generate those pulses in milliseconds. The issue lies in the discrete nature of the measured quantities and scan cycle intervals. When counting pulses over a fixed one-second timer cycle, aliasing can occur. For example, if a motor running just under 300RPM has 201ms between pulses, the speed calculation may vary based on when the first pulse is detected during the timer cycle. Measuring the time to reach a fixed number of pulses also introduces variability. For instance, at 300RPM, you may measure around 1000 ticks, while at 299RPM, this number could be 1003 ticks. PLC scan time and other delays can add noise to these measurements. To address this issue, it's crucial to determine desired accuracy, resolution, update rate, and range of speeds needed for accurate measurements. Considering factors like how long the motor can go without pulses before indicating a speed of 0 is essential for an effective approach to RPM calculations.
There are various versions of the QX40, with some offering high speed capabilities. By placing the module in the primary rack's initial slots, you can efficiently read pulses using interrupts, thus minimizing scan time. Alternatively, you can utilize the QD interrupt card. To activate interrupts, simply use the EI function followed by calling a subroutine for I0 (representing card 0) with an IRET instruction. This setup ensures smooth operation and faster data processing on the QX40.
Your setup seems feasible given the QX40's capabilities and the motor's max RPM. Since the rotation frequency of the motor at maximum speed (300rpm) is 5Hz, matching it with a QX40's response frequency of 1kHz, it should suffice as it is 200 times faster than the maximum rotation frequency. Consequently, there should be ample time to capture each rotation. Just remember to consider any potential latency in the system outside of the raw speed of the components, for a fool-proof setup.
Hi, given your setup, I think you're on the right track. The QX40's 1ms response time (which is indeed equivalent to a 1kHz response frequency) should be more than adequate for a rotating machine operating at up to 300RPM (5Hz). That would give you approximately 200 data points per rotation, providing robust data for accurate speed measurements. You've made sure that your proximity sensor can work effectively at the distance you require – another important consideration. Just make sure to check the compatibility of your devices with technological and environmental conditions to avoid any unexpected erroneous measurements. Good luck with your project!
Your proposed setup seems feasible to measure the speed of the motor generator accurately. Given that the motor rotates 5 times per second at max RPM, that equates to 200ms per rotation. With the QX40 using a 1ms response time (1000 times per second), there should be a sufficient number of readings within each rotation to accurately deduce the speed. Just remember, speed measurement accuracy will depend on the sensitivity of your proximity sensor and the consistency at which the motor maintains its RPM. You might consider conducting a few trials to gauge the accuracy of your setup. Always look out for any systematic error and correct it to improve your measurement accuracy.
It sounds like you have a well-thought-out setup! With the QX40 set to a 1ms response time, you're looking at a high enough sampling rate to capture the rotations accurately, especially since the motor isn't exceeding 5 revolutions per second at 300 RPM. Over one second, you'll be able to gather sufficient data points for a reliable speed calculation. Just make sure your proximity sensor is correctly positioned to detect each rotation without missing any; also, consider any potential noise or interference that might affect readings at those speeds. Overall, it seems promising—best of luck with your measurements!
It sounds like you're on the right track with your setup! With the QX40 set at a 1ms response time, you're looking at a frequency of 1kHz, which should definitely allow you to capture the proximity sensor's output accurately given that your motor generator will complete roughly 5 revolutions per second at 300 RPM. Make sure the proximity sensor's output can respond effectively within that timeframe, and you should be able to obtain a precise speed reading. Just keep an eye on any potential noise or interference from the motor, as that could affect your measurements. Good luck with your project!
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Answer: Answer: The accuracy of measuring the motor generator speed with a proximity sensor and the QX40 input card set at 1ms response time can be influenced by various factors such as the proximity sensor's precision, the motor generator's stability, and the configuration setup. It is recommended to test the setup and calibrate the system to ensure accurate speed measurement.
Answer: Answer: The Mitsubishi Input Card QX40 offers flexibility in setting response times (1ms, 5ms, 10ms, or 20ms) which can be beneficial for fine-tuning the speed measurement system. It provides a cost-effective alternative to high-speed counter modules while still offering reliable performance.
Answer: Answer: The distance detected by the inductive proximity sensor plays a crucial role in the accuracy of speed measurement. A shorter detection distance (5mm) may provide more precise readings, especially when monitoring high-speed rotations. It is essential to consider the sensor's specifications and adjust the setup accordingly for optimal performance.
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