Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-09-28
2001-10-16
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S678000, C327S514000
Reexamination Certificate
active
06304096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a measuring device for measuring the intermediate circuit voltage of a gradient amplifier of a magnetic resonance imaging (MRI) apparatus.
2. Description of the Prior Art
In a typical magnetic resonance imaging apparatus, a number of gradient coils (usually three gradient coils for the x, y and z axes, respectively) are employed to spatially encode the magnetic resonance signals arising from an examination subject after excitation of nuclear spins in the subject. Each gradient coil is operated by a gradient amplifier, and each gradient amplifier typically includes a number of intermediate amplifier circuits or stages. Ideally, it would be desirable to measure or monitor the intermediate circuit voltage of each of these intermediate circuits, however, due to their large number this is impractical for reasons of cost and complexity. An additional problem in measuring the intermediate circuit voltage under such circumstances is that this voltage is usually a floating voltage, i.e., it is not always referenced to a reference voltage or ground.
For these reasons, generally only monitoring of one voltage limiting value or two voltage limiting values takes place whereby a threshold detector is driven by a power Zener diode. If more information is needed, measuring circuits in the intermediate circuit connected parallel to the discharging resistor of the intermediate circuit capacitor are utilized. Such measuring circuits, however, are not only considerably more expensive and require considerably more outlay in terms of circuitry, but also still require an auxiliary power supply.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a measuring device for measuring the intermediate circuit voltage of a gradient amplifier, which is simply and inexpensively constructed and which does not need its own auxiliary power supply.
This object is achieved in accordance with the invention in a measuring device having a measuring circuit with a potential-dividing connection to a voltage indicating device, the measuring circuit being connected in series with the discharging resistor of the intermediate circuit capacitor and being driven from the discharging current via the discharging resistor.
Such a circuit is simply constructed and operates without an auxiliary energy supply. In a further embodiment of the invention a driver that is preferably fashioned as a transistor is driven via an astable flip-flop, this driver is connected to the low impedance path of a light-emitting diode that emits light at a frequency that is proportional to the intermediate circuit voltage. The intermediate circuit voltage is identified in an evaluating unit that contains a photoreceiver that detects the light pulses.
In a particulary simple inexpensive embodiment the astable flip-flop contains a thyristor tetrode that is driven via a voltage divider having a Zener diode lying connected in parallel with a capacitor that is connected in series with the discharging resistor. The thyristor tetrode simply fashioned by two interconnected transistors.
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Metjahic Safet
Nguyen Vincent Q.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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