Description of BS 90:1975 1975

1.1 This British Standard specifies requirements for direct-acting electrical recording instruments, which are used for recording the instantaneous, effective or mean values of one or more measured quantities as a function of time. It refers to strip, drum and disc recording instruments, such as

ammeters;

voltmeters;

single-phase and polyphase wattmeters, varmeters and phasemeters;

frequency recorders.

It applies to those recording instruments which incorporate rectifiers or diodes and to thermocouple recording instruments, also to certain accessories used with such apparatus, such as

shunts;

series resistors and impedances.

Other accessories may be associated with instruments provided that the instrument has been calibrated together with the accessory.

1.2 The standard also applies to electrically operated measuring equipments provided that the electrically operated recording measuring instrument (receiver) only is considered, and that the relationship between the non-electrical and the electrical quantity is known.

Additionally, it applies to recording instruments incorporating electronic devices in their auxiliary circuits.

1.3 The standard generally does not apply to recording instruments having electronic devices other than rectifiers or diodes in the measuring circuit.

However, at the choice of the manufacturer, recording instruments together with their non-interchangeable accessories having electronic devices other than rectifiers and diodes in the measuring circuit shall be considered as included in the scope of the present standard provided that they are marked “BS 90” and marked with the class index and the appropriate symbol from Table 17.

1.3.1 Examples include recording instruments together with non-interchangeable accessories, if any, having neither an incorporated supply source nor needing an external supply source. The electronic devices of these recording instruments are energized by the measured quantity and will, in some circumstances, be used for the protection of the recording instrument.

1.3.2 Examples also include recording instruments together with non-interchangeable accessories, if any, having an incorporated supply source, in general a battery, provided that the electronic devices are used for affecting the recorded value only, and that the voltage of the source and any voltage generated from that source do not exceed the limit of extra low voltage.

1.3.3 An external supply source is allowed when the nominal circuit voltage (circuit insulation voltage) of the measuring circuit does not exceed the limit of extra low voltage.

1.4 The standard does not apply to:

recording instruments having a square-wave response greater than 90 % of the effective range on a square wave with an amplitude equal to the effective range and a frequency of more than 5 Hz;

multi-purpose recording instruments and ohmmeters;

integrating recording instruments;

indirect-acting recording instruments;

recording instruments in which the measured quantity is presented in the form of digits, codes, punched cards etc.

recording instruments in which the chart movement is a function of a quantity other than time.

1.5 This standard does not contain requirements for protection against environmental conditions.

NOTE The titles of the British Standards referred to in this standard are listed on the inside back cover.

1.6 This standard does not specify requirements concerning dimensions of instruments or detailed requirements concerning terminal markings and diagrams of connection.

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