Speed transducer on vertical mill

[zoeper]

Hi,
I recently received my cnc mill but there seems to be a problem with the speed transducer. Mill is a Avon 3000 with an Anilam GXM controller (1992)
It uses a standard variable speed head with an electric motor that replaces the speed adjustment handwheel. It is fitted with a sensor that sits close to a metal gear in the head and it "counts" the teeth on the gear to give speed feedback to a speed controll card. Sensor has two wires and the front has a small magnet in the center.
1. What type of sensor is this?
2. How can i test if it's working properly (using a multimeter)
Thanx
Pieter

[gar]

061126-0752 EST USA

This is a magnetic sensor. Broadly it can be one of two types.

The first type has a coil wound around the magnet. This will have an AC output voltage proportional to speed. Thus, it is useful only down to some low speed. This is the kind of sensor used by Ford on on the rear differential for ABS sensing.

To test this type use an ohmmeter first and check resistance. This might be in the 1000 to 2000 Ohm range. If the resistance is very high, then the coil or internal connections are bad.

If the coil resistance looks good, then rotate the spindle at 60 RPM. The output might be on the order of 1 Volt. Change speed and the output should be proportional to speed.

The speed sensitive might have some other sort of magnetic sensor, but unlikely.

The other broad type will not be speed sensitive. This will usually use a Hall device, and requires more than two wires. Some other static magnetic sensors might use a two wire device, but unlikely.

I suspect you have the coil magnet type.

.

[Al_The_Man]

Originally Posted by gar 061126-0752 EST USA This will usually use a Hall device, and requires more than two wires. Some other static magnetic sensors might use a two wire device, but unlikely. .

Gar, there are many manufacturers that make 2 wire inductive proximity switches now.
The do not have the current capability of the 3 wire type, but supply enough current for PLC and for other electronic input.

Pieter, Is there any marking on the switch?
Al.

[gar]

061126-1129EST USA

Al:

I have not checked prox switches for response time, or ability to work with a small tooth gear.

If one assumes 60 teeth on the gear, then at 3600 RPM the output is 3600 Hz, and at 7500 RPM it is 7500 Hz, or at 50% duty cycle 67 microsec on and off.

Also prox switches have a broad field of view.

Have you used a prox switch with a small tooth gear for position or speed sensing? If so what one, and how sensitive to position was it?

.

[Al_The_Man]

Gar, Your right about the 2 wire prox being low on response time, too low for the application you mention, what I have used in the past for this is a Honeywell 1G101DC Hall-Effect tooth sensor, good for up to 100khz. This is three wire type.
The other component I have used for its miniaturization is the Allegro A1101 25khz, but this hall effect requires a 'Pill' magnet or multi-pole ring magnet for operation.
Otherwise for ordinary low response hall effect sensors, I use the 12mm barrel type, the detection field is narrower on these and even more if shielded type are used.

BTW Pieter, if you turn can turn the gear so it trips over one tooth and put a voltmeter on the two leads from the sensor, you should see a transition from close to 0v to whatever the supply for it is, typ. 5vdc to 24vdc.
Al.

[zoeper]

I had the sensor on a scope with the machine running and found the following:
Sine wave output of:
1250Hz 8.7V p-p @+-600RPM
2173Hz 11.5V p-p @1200 RPM
5000Hz 17Vp-p @3000 RPM
Sensor trace back fine to where it enters the speed controll card and is obviously not the problem.
P

[awright]

zoeper, sounds like your speed sensor circuit board has a problem. Here are some random thoughts on troubleshooting. These are just general principles, as I have not worked specifically on machine speed sensor circuits. Since you have a 'scope, troubleshooting should not be a major problem.

Does the card have an analog or digital readout to the controller or display? Can you post a photo of the card or at least a list of ICs and transistors on the card?

What you probably have is an analog amplifier/comparitor or a Schmidt trigger IC at the input from the sensor. You should be able to see an amplified or squared-up signal out of that input stage.

If the output is a linear analog signal proportional to speed, you will probably find the input stage is followed by a monostable pulse generator that puts out a constant amplitude/width pulse for each positive transition or each zero crossing of the incoming signal from the sensor. This would be followed by an averaging low-pass filter. The outputs from these are all easy to see on the 'scope. There could also be higher level ICs for which you might have to get spec sheets to interpret their condition.

If the output is digital, the incoming signal may disappear into a microprocessor and you would have to know more about the circuit/programming to go much further in troubleshooting.

Hope this gets you a little further along.

awright