CHAPTER 5.0 Functional Overview
5-66
CDS7324 (FORMERLY LSF-0819)
Rev. A
INSTALLATION & USER’S MANUAL
5.13 Self Protection
5.13.1 Power Amplifier Thermal Protection Mechanism
The power amplifier is protected by using a scheme called Thermal-Foldback. The DS2110 is rated to operate at
an ambient temperature of up to 40
°
C.
The Foldback scheme is designed to ensure a very conservative temperature margin is maintained between
power device manufacturer's rated maximum temperatures (semiconductor junction temperature) and the
actual semiconductor junction temperature.
The Running Thermal Limit applies when the speed of the motor is greater than approximately 50RPM. The
Stall Thermal Limit applies for motor shaft speeds of less than approximately 50RPM. The Stall Limit will
become less than the peak current capability of the amplifier only at elevated ambient temperatures and high
continuous operating loads.
5.13.2 Motor Thermal Protection Mechanism
The DS2110 can measure the temperature of the motor by means of a Negative Temperature Coefficient
thermistor (NTC) or a Positive Temperature Coefficient thermistor (PTC) buried within the motor windings.
With the motor NTC, temperature is measurable between approximately 25
°
C and 175
°
C.
The PTC acts as a thermal switch so linear temperature measurement of the motor is not possible. When this
device changes from a low impedance state to a high impedance state, the software will detect and report a
fault.
Software calculates the motor thermal limit based upon the motor windings temperature. The motor
protection scheme is intended to ensure that the temperature of the motor core will not exceed 155
°
C.
5.13.3 Cabling and Interconnect Protection Scheme
Each DS2110 model has a continuous current rating. The DS2110 operates an algorithm that limits the overall
RMS level of motor phase current appropriately, over a time window. This is intended to protect the connectors
and internal circuitry, which would otherwise be thermally over-stressed.
The DS2110 measures the motor phase currents at a high frequency. It calculates the remaining amount of
current for the next period to ensure that the overall RMS current rating of the drive is not exceeded.
5.13.4 Regeneration Resistor Protection Scheme
The DS2110 can be equipped, depending on the model size, with an internal or external regeneration resistor.
The algorithm controlling the duty cycle of the resistor ensures that the power dissipated by the resistor is
maintained at the resistor rating provided by the user.
