The invention relates to a plug-in unit assembly comprising instrument transformers, a case assembly (1) comprising a connector assembly (10), and a plug-in unit (2) comprising at least one instrument transformer (3, 4) and configured to be connected to the case assembly (1). The instrument transformers (3, 4) of the plug-in unit (2) are coded in such a manner that the codings of the current transformers (3) and the voltage transformers (4) are different. The connector assembly (10) of the plug-in unit assembly of the invention is capable of identifying the type of the instrument transformers (3, 4) and based on their coding when the plug-in unit (2) is being connected to the case assembly (1).

A meter reader 12 analyzes a signal from a meter 22 and compares its structure with a plurality of known signal structures stored in a memory 41. If the comparison shows that a particular one signal structure stored in the memory is inconsistent with the data signal being received, that structure is rejected and not used in future comparisons as the receipt of the data signal progresses. Eventually, the non-rejected signal structures should be reduced to a single structure which by elimination must be the closest structure to that of the signal being read. The meter reader can then pass the received data signal and the identification of its particular signal structure to further processing apparatus 11 such as a signal recorder or signal display and can arrange this recording or display so that parts of the signal representing different properties can be arranged consistently with other data signals which may be of different structures.

A control circuit comprising a thyristor and a feedback circuit formed by an inductance and a generator for producing electrical energy in response to a luminous event. The feedback circuit controls the conducting or cut-off state of the thyristor by the fact that a trigger-gate of the thyristor is connected to a terminal of the generator having a polarity cutting off the thyristor when the generator is illuminated. The thyristor is switched on in response to an energy stored in the inductance, which energy is caused by a sudden discontinuity of the luminous event.

A method and apparatus for metering electrical energy with a meter having a base of a given configuration is shown to include a data member, attached to the base, for providing a data signal, at least a portion of which is representative of the base configuration, and a processor, connected to the data member, for comparing the meter base configuration to a reference configuration and for providing an indication signal whenever the meter base configuration and the reference configuration do not match. If the data member generates a serial data signal of digital words, it is desireable for a number of bits in each serial communication to be representative of the meter base configuration. Such a serial data signal is achieved if an input/output expander having a plurality of inputs is utilized. In such an embodiment, it is preferred to provide digital signals representative of the meter base configuration to select inputs of the expander. Such digital signals can be provided by first and second voltage sources, representative of logic high and logic low. In an especially preferred embodiment the processor is a register having a micro-processor and a display. The microprocessor compares the data signal to the reference configuration and generates a message displayed on the display whenever the meter base configuration and the reference configuration do not match.

A meter (10) is capable of use with a plurality of different sensor heads (16, 16b). The reading meter (12) includes a digital display (20), a processor (22) and memory (23), and an analog-to-digital converter (ADC 41). Each different sensor head includes a memory (32a) which carries at least the processing algorithm for the particular sensor. In operation, the reading meter (12) reads the detector head memory (32a), and loads the information so read into its processor memory (23). The raw sensor data is converted to digital form, and processed in accordance with the stored algorithm, to produce the desired display. In one embodiment, the detector head memory (32a) is read, and the information is serially coupled to the reading meter. In another embodiment, the serial data is converted to optical signals (634) for transmission. The processor memory (23) may include other data which is held in semipermanent storage, such as calibration data for an ADC within the reading meter, and housekeeping information for the display (20). A count-down counter (52) in each sensor head is preprogrammed with a number representing the number of days remaining in the calibration period, and is decremented daily.