I have built a circuit board to change the PWM output from Mach3 into a 0-10v signal required by my DC motor controller. The board is based on a couple of designs that are readily available on the internet and the DC controller is a Control Techniques Lynx 08 that was fitted to my machine in its original condition. The Lynx is around 20 years old but works fine.
The Lynx has its own on-board 10V supply that is used for external speed control via a potentiometer. See extract from handbook below, fig2 Basic connection.
Connecting up a simple 10k Ohm potentiometer gives me a full speed range from close to zero up to 2950rpm which I have measured using a calibrated handheld laser tachometer.
When I connect the PWM circuit board and control via Mach3 "S3000" the maximum speed that get drops down to around 2250rpm. I have my oscilloscope connected to the designated output and can see a good square wave as expected (actually a continuous high line for full speed). Measuring the input voltage at the Lynx, however, I can only see a maximum of around 7.5v which makes sense as this is proportional to the voltage at full speed.
So I guess the problem is something to do with loss of voltage, possibly over the resistors, within the board, but as I don't have a full understanding of how the board works it makes it difficult to come up with a solution. I have tried changing the resistor values at various points, and adding a potentiometer into varios parts of the circuit for experimentation purposes but without success. I felt comfortable doing this without damage to the Lynx as the 10v originated from the Lynx.
So, if anyone with a better understanding of whats going on in this circuit, and how I can get my 10v out for max speed, I would really appreciate your advise.
Thanks ...Sweep