circuit help requested, proximity probe

[William Gilmore]

I'm trying to figure out the spindle speed sensor on an 80s cnc mill.  In another drawing it's referred to as a proximity probe.  In the attached drawing it's on the left size with the BRN and BLU wires.  In the head of the mill the probe reads a toothed wheel.

To my untrained eye it looks like the BRN wire gets +9V and the BLU wire is the signal.  Put 9 volts to the wire and see what happens?  I don't want to fry this thing as it's nicely integrated in to the machine.

The controller I'm using can take 4-24V inputs so I think if I can get a pulsing signal from the sensor I can take it from there.  Do I need the decoupling cap?

Thanks.

[Dan Lavin]

I think that what you have is a magnetoresistive gear tooth sensor. If
it were a hall effect sensor, it would have more than two leads.

Try putting an ohmmeter across it. If you get a reading, see if it
varies in the presence of a magnet or ferrous material. If it does, you
can select a load resistor accordingly. The 1k and 330 ohm resistors
near Q1 function as a load in your schematic.

You will definitely need a load resistor, but you will need a decoupling
capacitor only if DC bias prevents you from reading the signal.

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[William Gilmore]

Put ohmmeter across the wires and turned the spindle by hand.  Constant OL (open circuit).  I found this : http://pewa.panasonic.com/news/e-news/article/sunx-two-wire-inductive-proximity-sensors%3A-the-universal-donor which has the same wire colors and suggests that it would need power to work.  Should I recreate the circuit from the original drawing?

On Wed, May 1, 2013 at 2:07 PM, Dan Lavin <dan...@verizon.net> wrote:

I think that what you have is a magnetoresistive gear tooth sensor. If it were a hall effect sensor, it would have more than two leads.

Try putting an ohmmeter across it.  If you get a reading, see if it varies in the presence of a magnet or ferrous material.  If it does, you can select a load resistor accordingly.   The 1k and 330 ohm resistors near Q1 function as a load in your schematic.

You will definitely need a load resistor, but you will need a decoupling capacitor only if  DC bias prevents you from reading the signal.

On 5/1/2013 11:59 AM, William Gilmore wrote:

I'm trying to figure out the spindle speed sensor on an 80s cnc mill.  In another drawing it's referred to as a proximity probe.  In the attached drawing it's on the left size with the BRN and BLU wires.  In the head of the mill the probe reads a toothed wheel.

To my untrained eye it looks like the BRN wire gets +9V and the BLU wire is the signal.  Put 9 volts to the wire and see what happens?  I don't want to fry this thing as it's nicely integrated in to the machine.

The controller I'm using can take 4-24V inputs so I think if I can get a pulsing signal from the sensor I can take it from there.  Do I need the decoupling cap?

Thanks.

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[Dan Lavin]

It looks like you have identified the part.

 I would replicate the circuit with R11, R12 and C2.  If that gives you enough to trigger your circuit, that's it; if not, replicate the rest of the Q1 circuit up to pin 1 of the LM2719.  If you have a scope, look at the signals to see what's going on.

On 5/1/2013 5:18 PM, William Gilmore wrote:

Put ohmmeter across the wires and turned the spindle by hand.  Constant OL (open circuit).  I found this : http://pewa.panasonic.com/news/e-news/article/sunx-two-wire-inductive-proximity-sensors%3A-the-universal-donor which has the same wire colors and suggests that it would need power to work.  Should I recreate the circuit from the original drawing?

On Wed, May 1, 2013 at 2:07 PM, Dan Lavin <dan...@verizon.net> wrote:

I think that what you have is a magnetoresistive gear tooth sensor. If it were a hall effect sensor, it would have more than two leads.

Try putting an ohmmeter across it.  If you get a reading, see if it varies in the presence of a magnet or ferrous material.  If it does, you can select a load resistor accordingly.   The 1k and 330 ohm resistors near Q1 function as a load in your schematic.

You will definitely need a load resistor, but you will need a decoupling capacitor only if  DC bias prevents you from reading the signal.

On 5/1/2013 11:59 AM, William Gilmore wrote:

I'm trying to figure out the spindle speed sensor on an 80s cnc mill.  In another drawing it's referred to as a proximity probe.  In the attached drawing it's on the left size with the BRN and BLU wires.  In the head of the mill the probe reads a toothed wheel.

To my untrained eye it looks like the BRN wire gets +9V and the BLU wire is the signal.  Put 9 volts to the wire and see what happens?  I don't want to fry this thing as it's nicely integrated in to the machine.

The controller I'm using can take 4-24V inputs so I think if I can get a pulsing signal from the sensor I can take it from there.  Do I need the decoupling cap?

Thanks.

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[James Marquardt]

If you look at the datasheet for the LM2917 pages 9 and 13 have the same basic circuit that you have posted minus transistor Q1 which is being used in your circuit simply as an inverting buffer.  You will need a load resistor of about 1k to ground and the other lead can go to +9v just like in the circuit.  So, connect the BROWN wire to +9 and the BLUE wire to the 1k resistor and then the other side of the resistor to ground.  Place your voltmeter on a low dc volts scale across the resistor and turn the spindle by hand.  the meter should bounce from ground to vcc and back as the spindle is turned.  If you have an oscilloscope you will have a much better way to see this happening and also be able to run the spindle from the motor as opposed to turning by hand.  In your circuit the LM2917 is a Frequency to Voltage converter which is outputting a voltage proportional to the input frequency EXAMPLE: 1khz in equals 1 volt out.  For arguments sake the 1khz could be the spindles RPM so 1volt out means the spindle is spinning at 100RPM.

So if you follow my connection above with the 1k resistor you will not blow the sensor up.  And take a look at the datasheet for the LM2917.  It can answer many questions you have.

Here it is:
http://www.ti.com/lit/ds/symlink/lm2907-n.pdf

Regards,
JIm