| 摘要 |
A device is provided for a meter having an indicator, e.g. a pointer, and which detects the presence or absence of the meter pointer at one or more set points or between two set points. The device does not alter the operation of the meter and may be coupled to an alarm or other signal, or it may be used to actuate a mechanism under control of the meter. The device comprises at least one light-emitting diode which produces radiation which falls on a specific area of the meter face and on the meter pointer (if it is within that area) and is reflected from the meter face (and the pointer) to a phototransistor or other suitable receiver which "reads" the signal produced by the radiation reflected from the meter face and the pointer, if present in the area read. The device is mounted so that it can be moved to any desired area of the meter face. Preferably the device is mounted externally to the meter. However, it may be enclosed within the usual meter housing, without altering the operation of the meter.
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