How Speed limiting works on the Centrifugal Extractor :
A balance sensing board is used to monitor an accelerometer. The thresholds of acceleration or "out of balance" (OOB) are set in software. The accelerometer is set to 2.5 VDC when at rest. See
Setting the Proper Voltage on Accelerometer for Centrifugal Extractors article for more details.
When the machine starts accelerating the software looks for a 100 mV peak to peak waveform over 300 ms. The output for "allow acceleration" is turned off if the board does not see this amplitude. If we see 100 mV, then we can assume the accelerometer is working. Output is turned on for allow acceleration.
The inverter also has an output contact triggered by the frequency set in constant L4-03. This was set to 80 (now 100 as of January 2020) which turns on this output when we hit this frequency. If you set this value too low, the accelerometer may not see enough force to trigger the "accelerometer checking" code. A "perfect load" would not extract at high speed if you set the value too low. Lower speeds may not produce enough force to trip the threshold and we would clamp the final speed to the setting in L4-03 by making the "do not accelerate" input to the input board on the .
If the balance board and the inverter outputs are on then the machine cannot accelerate. So, if the accelerometer is broken then we limit speed at approximately the value in L4-03.
Full range of the accelerometer is different for a washer extract than an extractor.
For a washer extractor: 1 Volt per G (1V/G). At 2.50VDC we have 0 G's. At 4.50VDC accelerometer output we see 2 G's.
For an extractor: 500mV per G (500mV/G). At 2.50VDC we have 0 G's. At 3.50VDC accelerometer output we see 2 G's.
The only relay we use on the balance board is K3. If we see a threshold limiting force for 3 samples then we turn on the output. If we do not see 100 mv P-P wave then the relay is on. So, you will see the relay on until it sees 100 mv P-P and then turn off. If the OOB is too large then the relay turns on and the machine stops acceleration.
The inverter contact is in series with the balance board contact to allow acceleration if both outputs are on.
The input for do not accelerate is MTA 38-6 on the processor board.
See the attachment for the schematic and jumper settings for the board. The jumper basically desensitize the board and allow the unbalance to pass without slowing the cylinder.
The real test is with a 15% imbalance. So, a 40 pound imbalance (like a bag of goods, not loose goods, at 40 pounds dry) on a 48040 extractor should prevent high speed. We expect a 15 % reduction in speed at this 15% OOB weight. The goods must be in a tight bag and not able to distribute. Do not just run a load of normal goods and expect any type of qualitative test.
Jumper settings are shown below. You set the jumper to get a 15% reduction in speed with a 15% OOB. More reduction would not hurt the machine.
