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NI ISM-7400 User Manual
Configuring the NI ISM-7400
Setting the Current
Set the current to 100% to achieve maximum torque. However, under some conditions you
might want to reduce the current to save power or lower motor temperature. This is important if
the motor is not mounted to a surface that will help it conduct heat away or if you expect the
ambient temperature to be high.
Step motors produce torque in direct proportion to current, but the amount of heat generated is
roughly proportional to the square of the current. If you operate the motor at 90% of rated
current, you will get 90% of the rated torque and approximately 81% as much heat. At 70%
current, the torque is reduced to 70% and the heating to about 50%.
Switches 1 and 2 on the front of the NI ISM-7400 control the percent of rated current that will
be applied to the motor. Set them according to the illustration below.
Figure 18.
Configuring Current on Switches 1 and 2
Setting Idle Current
You can also reduce motor heating and power consumption by lowering the motor current when
it is not moving. The NI ISM-7400 automatically lowers the motor current when it is idle to
either 50% or 90% of the running current. The 50% idle current setting lowers the holding torque
to 50%, which is enough to prevent the load from moving in most applications. This reduces
motor heating by 75%. Some applications, such as those supporting a vertical load, require a
high holding torque. In such cases, set the idle current to 90% as shown in the following figure.
Figure 19.
Configuring Idle Current on Switch 3