LT360 Precision Turntable
User Manual
LT360 Precision Turntable
User Manual
36
The LT360 samples the analog input and then begins a rotation to the
indicated position. While it is moving the analog input is ignored. When it
reaches that position and stops, it then samples the analog input again, and
the process repeats.
It is critically important that the voltage source be of low noise and highly
stable. Since the LT360 responds to resolutions of 1mV (0.1deg), all noise
and hum must be kept below 500uV. The DC accuracy of the source must
also be better than ±500uV.
■
Analog Output
This BNC connector provides a means to obtain an analog control voltage
from the LT360 at all times. This can be useful if driving some other display,
chart recorder, or other plotting device.
The scale factor is 10mV/deg, and the resolution of the LT360 is 0.1 degree.
Therefore, the step size and/or resolution of the analog voltage will be 1mV.
The actual output circuitry is single ended, but it is highly recommended that
the other device input be differential to help reject ground noise. It should
have at least 100K Ohm input impedance to prevent loading errors. The
output voltage range can either Unipolar (0..+3.600) or Bipolar (0..±1.800)
as selected in the software or by commands, with different operating modes.
The Analog Output voltage is extremely precise and highly stable over the
entire temperature range of 0C to 40C.
53
For a Standard LT360 model the maximum platter driving torque is 49NM
and for the HiTorque model 76NM (Newton•Meters). We will assume that
the rotational velocity is set to 1 RPM, and that the Flat acceleration function
is in use.
From the graphs on the previous pages we find that the average accelera-
tion for the Flat function is about 0.21M/S
2
at 1 RPM and 1 Meter, assuming
the rotation step is at least 3.2 degrees. Therefore the maximum mass load
which can be rotated is:
Standard LT360, 1Meter, 1RPM, Flat Profile, Travel
≥
3.2 Degrees
M=T/(R•A) = 49/(1.0•0.21) = 233kg = 513 lbs
HiTorque LT360, 1Meter, 1RPM, Flat Profile, Travel
≥
3.2 Degrees
M=T/(R•A) = 76/(1.0•0.21) = 362kg = 796 lbs
The mass load capability for other operating conditions can also be calcu-
lated as easily. It should be noted that the acceleration is proportional to
the square of RPM. Reducing the RPM by a factor of 2, reduces the accel-
eration by a factor of 4. Thus the mass load capacity is increased by a factor
of 4.
The acceleration scales linearly by radial distance. Reducing the distance by
half reduces the acceleration by half. However, the radial distance also
appears again in the equation by itself. Therefore, reducing the distance by
a factor of 2 actually increases the mass load capacity by a factor of 4.
