Mach-DSP User’s Manual
Document Number: MACH-DSP-9021
Page 59
www.ScannerMAX.com
to be exerted by the Mach-DSP. Therefore when the X-Y mount and environment are all
well-known and controlled, or when input command waveform is never expected to
cause scanner heating (for example, in laser marking or other small-signal applications),
the first mode (Calculate by RMS current) should be chosen. (Note that the precision of
the coil temperature calculator is greatly enhanced when using a thermistor attached to
the X-Y mount, as described in Chapter 3.5 of this manual.)
Coil resistance at 25 degrees C
Enter the coil resistance as specified on the scanner’s datasheet.
Current-filter time constant
The RMS calculation requires a time constant over which to average the RMS current.
This is unitless, and may be fine-tuned by using the built-in oscilloscope while observing
the Coil Temperature (TP22). As the value increases, the speed of the filter also
increases (i.e. the amount of time over which the current is averaged decreases).
Setting this to a value of 300 to 1000 is reasonable for ScannerMAX galvanometers.
Thermal resistance (degrees C per watt)
When the X-Y mount is a compression-style mount that is supplied by Pangolin, and it is
bolted to a large aluminum heat sink, then you can enter the thermal resistance as
specified on the scanner’s datasheet. Otherwise, you should enter a higher number to
take into account the sub-optimal mounting.
Current sense plus cable resistance (ohms)
When the Coil Temperature Calculator is operating in Mode 2, the Mach-DSP must
know the total resistance to expect, including not only the resistance of the scanner’s
coil, but also any additional resistance such as that of the current sense and even the
cable that connects the scanner to the servo driver.
The Mach-DSP uses a 0.1 ohm current sense resistor. A short cable may add an
additional 0.1 ohms, but a longer cable may add an additional 1 ohm.
You should enter the value corresponding to the cable resistance, and then add 0.1 to
that number to account for the built-in current sense resistor.
Coil inductance (micro henry)
Enter the coil inductance found on the scanner’s datasheet.
Back EMF Voltage
Enter the Back EMF voltage found on the scanner’s datasheet.
