SECTION 6: T200 FUNCTIONAL OVERVIEW T200 User's Manual
PAGE 6-61
6.9 Self Protection
6.9.1 Sources of Torque Limits
There are three sources of torque limitation within the T200:-
1. Programmable Torque Limits:- The user may program Automatic_Mode and Manual _Mode Torque_Limits.
These are described in Section Automatic and Manual Power Settings.
2. Analog Torque Limit:- The Spare Analog Input is used as a means of reading in a analog torque limit command.
This is described in Section 6.6.3 Position Mode.
3. Thermal Torque Limits:- The T200 provides a comprehensive thermal protection of the motor, the power
electronics and cabling and interconnect. These are described below in greater detail.
The minimum of these sources at any time is used to limit the available current. Note however that the Limit_Active
digital output function will only activate when the current demand is greater than a Thermal-Limit. This is because the
other limits are set by the user anyway.
6.9.2 Power Amplifier Thermal Protection Mechanism
The power amplifier is protected by using a scheme called Thermal-Foldback. The T200 is rated to operate at an
ambient temperature of up to 55° 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.
6.9.3 Motor Protection Thermal Protection Mechanism
§ The T200 measures the temperature of the motor by means of measurement of the Negative Temperature
Coefficient thermistor buried within the motor windings. The motor temperature is measurable between
approximately 25° C and 175° C.
§ 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.
6.9.4 Cabling and Interconnect Protection Scheme
Each T200 model has a continuous current rating. The T200 operates an algorithm that limits the overall RMS level of
motor phase current appropriately, over a time window that extends over the last averaging period. This is intended to
protect the connectors and internal circuitry, which would otherwise be thermally over-stressed.
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