AE4-S02 Spacecraft Mechatronics Displacement Sensors Dr. ir. W. Jongkind
TU-Delft
2004 – 2005
AE4-S02 Spacecraft Mechatronics Displacement Sensors Dr. ir. W. Jongkind
TU-Delft
2004 – 2005
Introduction (1)
Potentiometers. Linear as well as rotary potentiometer are applied.
Potentiometers are used in situations where accuracy is not of major importance,
Accuracies may vary from 0.3 % to 5 %.
Device is normally cheap.
Incremental Encoders.Linear and rotary incremental encoders are applied.
Rather inexpensive devices.
The performance depends on the resolution of the encoder slit pattern.
They can can be very accurate indeed.
Introduction (2)
Absolute Encoders. Again linear and rotary absolute encoders exist
The code pattern is in the majority of cases a Gray code pattern, binary code patterns are much less common
Electrical Transformers
For very accurate linear displacement measurements often Linear Variable Differential Transformers (LVDT)are applied
The rotary displacement can be accurately measured with rotary electrical transformer devices such as the Resolver or Synchro
Making the Right Choice
The following requirements and constraint should be addressed:
Required resolution
Required accuracy
Environmental constraints
Integration aspects
Availability
The selected displacement sensor is the most important factor and deciding for overall performance of a system especially when the device forms part of a feedback loop
Potentiometer (1)
Operating range from 1 mm to 1m
Potentiometer (2)
Encoders
Typically used as shaft angle encoders
The device output is in digital form
Digital output needs in general to be transformed with the aid of a computing device to obtain magnitude and direction of movement as well as position or angle information
Consist of a pattern impressed upon a part of the system that characterizes the motion
Two main classes of optical encoders:
Absolute encoders and
Incremental encoders
For velocity measurement nearly always incremental encoders are applied
Incremental Encoder
Readout System
Sense of Rotation
Linear Encoder Codes
Circular Encoder Codes
Gray Encoder Output
Encoder Construction
Incremental Encoder Construction
Gray EncoderConstruction
Incremental Encoder
Transformer Based Displacement Sensors
Linear Variable Differential Transformer
Synchro’s and Resolvers
Comments