Contactless Rotor Displacement Sensor Bridge Circuit
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Contactless electromagnetic sensors used for measuring rotor displacements in machinery face challenges such as susceptibility to temperature errors due to impedance changes in long connecting cables, limited operating conditions, and inaccuracy in distance measurements, especially in harsh environments like large rotary machines.
Innovation Solution
A sensor device with a bridge circuit configuration using two sensing coils and an input transformer, where the sensing coils are connected to the secondary windings of the transformer, allowing for separate excitation and detection signals, reducing sensitivity to cable impedance changes and enabling the use of long cables, and incorporating impedance matching elements to match cable impedances, thereby minimizing reflections and transmission losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If long connecting cables are used to connect the transducer to the signal processing circuitry, then the sensor can be used in large rotary machines with separated components, but temperature errors and impedance changes cause inaccurate distance measurements
Solution Approach 1:
A bridge circuit is introduced as an intermediary between the sensing coil and the signal processing circuitry. The bridge circuit includes the sensing coil, a reference coil, and balancing impedances arranged in a Wheatstone bridge configuration. This intermediary structure allows the use of long cables while compensating for their impedance changes through the bridge's differential measurement capability, thereby maintaining measurement accuracy despite cable temperature variations and impedance drift.
Solution Approach 2:
The patent employs a bridge circuit that measures differential impedance changes rather than absolute impedance values. By using a reference coil with identical cable connections and arranging both coils in a bridge configuration, the system changes the measurement parameter from absolute impedance to differential impedance ratio. This parameter transformation eliminates the effect of cable impedance changes on the measurement, enabling accurate distance measurement even with long cables subjected to temperature variations.
2Device complexity
If single-coil transducers are used, then the device complexity is reduced, but the sensor becomes susceptible to temperature errors and cable impedance changes
Solution Approach 1:
The single-coil transducer is segmented into two separate coils: a sensing coil that interacts with the rotor target and a reference coil that does not. Each coil has its own cable connection to the signal processing circuitry. This segmentation allows the bridge circuit to differentialize the measurement, canceling out common-mode temperature errors and cable impedance changes while preserving the differential signal that contains the actual distance information.
Solution Approach 2:
The bridge circuit serves as an intermediary that processes the outputs from both the sensing coil and reference coil. By introducing this intermediary processing stage, the system transforms two separate single-coil measurements into a differential measurement that is immune to common environmental disturbances, thereby improving reliability without significantly increasing overall system complexity.
3Adaptability or versatility
If encapsulated transducers are used to withstand adverse conditions, then the operating range under harsh conditions is improved, but the constructive efforts and integration complexity increase
Solution Approach 1:
The bridge circuit acts as an intermediary that enables the transducer to operate reliably in harsh conditions without requiring complex encapsulation. By using the bridge configuration with a reference coil, the system inherently compensates for environmental effects, allowing simpler transducer designs to achieve the same robustness that would otherwise require complex encapsulated structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution allows for accurate and reliable measurement of rotor displacements with reduced sensitivity to environmental changes and cable length, enabling the use of long cables and improving the ruggedness of the sensor design.
Implementation Method 1
each coil configured to interact with a surface of the rotor to detect displacements of the rotor relative to the first and second sensing coils
Implementation Method 2
an input transformer having a primary winding and at least a first and a second secondary winding, the primary winding of the input transformer forming an input for an excitation signal; wherein the first sensing coil, the second sensing coil and the secondary windings of the input transformer are connected to form a bridge circuit
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A contactless electromagnetic sensor device for determining displacements of a rotor (120) is disclosed. Two sensing coils (612, 614) interact with surfaces of the rotor. A bridge circuit is formed by the sensing coils and by two secondary windings (212, 213) of an input transformer (210). The primary winding of the input transformer receives an excitation signal. An output signal is obtained at an output tap formed by a common node between the sensing coils (612, 614) and a common node between the secondary windings of the input transformer. In this manner excitation and detection are separated. If cables are used for connecting the bridge circuit to signal processing circuitry, the input and output impedances of the bridge circuit can be matched to the characteristic impedance of the cables. An output transformer can be connected to the output tap. The roles of the input and output transformers can be interchanged.