Hi,

I'm hoping someone is able to help me regarding the following problem and thanks in advance.

I am using the PTO function on the ML1100 to drive a Baldor DSM 17 Stepper motor via a phoniex opto isolator. The Phoniex contact (PLC-OSC-24V/24V/2) has a frequency limit of 300 hz so I have set my PTO function file to a max frequency of 250 hz. The trouble is when I send a step output of 20 pulses I don't seem to get 20 steps on the baldor motor.

I have attached a circuit diagram for ease of explaining (please excuse the messy writing but its 3 am when im writing this!!) The stepper motor inputs are wired as sinking as I have no choice hence the need for the opto isolator and the 24V reference voltage and forward current limiting resistor. I have setup my stepper motor to give 6400 steps per revolution however for one revolution I seem to get 2000.

I have tried turning back the pto frequency to 10 hz but seem to get a few more steps (2300).

Has anyone tried anything similar? Any thoughts as to what may be causing this would also be appreciated?

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Hard to judge without knowing the drive input circuitry.
But don't you need a current limiting resistor on the optocouple input?

Thanks for your reply.

I have a 2.7k ohm resistor in to limit the forward current to a nominal 8 mA. I did notice in the latest Baldor manual (DSMS series) that it makes no metion of requiring this resistor but still shows it in the wiring diagrams. In the old manual (DSM Series) they point it out with a warning about limiting the current and give suggested resistor values. Could this potentially be affecting my step input? I dont want to run the risk of removing the resistor and blowing the input.

You stated that the stepping drive is configured as a sinking input. Therefore, the device that drives this input must be a sourcing output. The schematic you have drawn shows a sinking output, not sourcing. Therefore, it will not work properly. On the opto-isolator output, you need to attached +24V to the collector and the emitter will then feed the input to the stepping drive. You may or may not need a pull down resistor on the input to the stepping drive.

On the DSM series (other than the 34 frame) the opto-reference should typically be supplied with +5Vdc (the 34 frame will take +5V to +24Vdc without any additional current limiting).
If you are going to use +24Vdc to power the opto-reference on the 17/23 frame models you need to fit a current limiting resistor on the step/direction signals to limit the current to 7mA (in your case you've limited it to 8mA - this is fine, it won't die unless the current goes above 15mA).

(The DSMS series is a little different - see http://www.baldor.com/downloads/manuals/_d...N1940_01-07.pdf[/url])

You seem to have wired everything correctly (according to your schematic) so things I would check are...

(a) Do you have another opto-isolator to try?
(b) Is the 0V on the DSM logic side of the opto-isolator (i.e. the 0V for the 24Vdc wired to the opto-reference) the same 0V as used for the motor power? (I've had problems when it isn't)
© What settings do you have MRC and MHC on the DSM (run current and hold current)?

You can always e-mail motionsupport.uk@baldor.com for further assistance
;)