US 4,229,102 AGranted

Method and apparatus for balancing out disturbances in distance measuring systems

AssigneeAGA Aktiebolag

InventorsKlas R. Wiklund, Lars A. Ericsson

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Abstract

A method and apparatus are provided for balancing out interference caused by stray coupling between the internal circuits of a distance measuring apparatus of the phase-type in a simple manner which produces a substantial increase of the usable measuring range. At least two groups of mutually separate distance measurements are performed, with each group including at least one measurement operation. For each pair of groups of distance measurements, one measuring group is effected with the transmitter signal in a first phase and the other measuring group is effected with the transmitter unit of the transmitter section supplied with a transmitter signal in a second phase which is displaced substantially 180.degree. relative to the first phase. The mean value or the mean values of the measuring results in each measurement group are thereafter formed, with this calculation being made either by hand or automatically. Preferably, the invention includes a controllable phase shifter to provide the phase shift of the measurement signals supplied to the transmitter.

Claims13

Dependent claims

A method of balancing our interference caused by stray coupling between the internal circuits of a distance-measuring apparatus of the phase-type having a receiver section and a transmitter section, wherein a phase measurement operation is carried out which comprises an external phase measurement wherein a modulated electromagnetic signal is transmitted from the transmitter, reflected by a measurement target and received by a receiver section, and a reference measurement wherein a electromagnetic signal of the same frequency and phase of the first mentioned signal is transmitted from the transmitter section to the receiver section over an internal path of known length for comparison with the signal received by said receiver section during the external phase measurement;

wherein at least two groups of separate distance measurements, each comprising at least one said phase measuring operation, are carried out;
wherein for each pair of groups the one measuring group is effected with the transmitter unit of the transmitter section supplied with a transmitter signal of a first phase, and the other measurement group is effected with the transmitter unit of the transmitter section supplied with the transmitter signal of a second phase which is displaced substantially 180.degree. relative to the first phase;
and the mean value being formed of the mean values of the measuring results in each measurement group, a control unit being used to control switching between the external phase measurement and the reference measurement during each phase measurement operation and to control switching the phase of the transmitter signal between said first phase and said second phase during alternate measuring groups.

A distance measuring apparatus of the phase-measuring type for making at least two groups of distance measurements and comprising a receiver section and a transmitter section including a transmitter unit, wherein a phase measurement operation is carried out which comprises an external phase measurement wherein a modulated electromagnetic signal is transmitted from the transmitter, reflected by a measurement target and received by a receiver section, and a reference measurement wherein a electromagnetic signal of the same frequency and phase of the first mentioned signal is transmitted from the transmitter section to the receiver section over an internal path of known length for comparison with the signal received by said receiver section during the external phase measurement, said apparatus further comprising a controllable phase-shift means for reversing the phase of the measurement signal for the transmitter unit of the transmitter section for each of the said at least two groups of measurements so that the phase of the measurement signal for one group is reversed with respect to the phase of the measurement signal of another group, said apparatus further comprising a control unit for controlling switching between the external phase measurement operation and for controlling switching the phase of the transmitter signal between said first phase and said second phase during the two measuring groups.

Dependencies are inferred from the claim text.