BS 89-8:1990 pdf free download.Direct acting indicating analogue electrical measuring instruments and their accessories — Part 8: Specifleation for special requirements for accessories.
1 Scope
1.1 This sub-clause of Part 1 does not apply to
accessories.
1,2 Part 8 of the standard applies to accessories as
defined in Sub-clause 2.1.15 of Part 1.
1.3 This sub-clause of Part 1 does not apply to
accessories.
1.4 to 1.8 See Part 1.
2 Definitions
See Part 1.
3 Description, classification and
compliance
3.1 Description
Accessories shall be described:
3.1.1 According to their nature as:
3.1.1.1 Shunts as defined in Sub-clause 2.1.16 of
Part 1.
3.1.1.2 Series resistors (impedances) as defined in
Sub-clause 2.1.17 of Part 1.
3.1.1.3 Special-to-type accessories, for example reactor boxes for frequency meters.
3.1.2 According to their interchangeability as:
3.1.2.1 Interchangeable accessories as defined in Sub-clause 2.1.15.1 of Part 1.
3.1.2.2 Accessories of limited interchangeability as defined in Sub-clause 2.1.15.2 of Part 1.
3.1.2.3 Non-interchangeable accessories as defined in Sub-clause 2.1.15.3 of Part 1.
3.2 Classification
3.2.1 Interchangeable accessories and accessories of limited interchangeability shall be classified in one of the accuracy classes denoted by the following class indices:
0.02, 0.05, 0.1, 0.2, 0.3, 0.5, 1, 2*, 5*, 10*,
NOTE The class indices marked with an asterisk are only for use with high-voltage series resistors and impedances.
3.2.2 A non-interchangeable accessory has no accuracy class of its own: the accuracy class of the associated instrument applies to the combination of the instrument and accessory.
3.3 Compliance with the requirements of BS 89-8.
See Part 1.
3.3.1 and 3.3.2 See Part 1.
3.3.3 Interchangeable accessories and accessories of limited interchangeability
3.3.3.1 The error shall not exceed the amount specified by Subclause 4.2 at all values of the measured quantity up to and including the rated value.
3.3.3.2 Shunts and series resistors shall be tested using direct current unless a frequency is stated.
3.3.3.3 Interchangeable shunts
When the current taken by the associated measuring instrument is smaller than the rated current multiplied by the class index of the shunt and divided by 300. the current taken by the associated measuring instrument may be neglected.
3.3.4 Accessories of limited interchangeability
3.3.4.1 The accessory is connected to an instrument of the associated type and the errors of the combination are determined.
3.3.4.2 The instrument alone is tested under the same conditions as used in the test of Sub-clause 3.3.4.1 and its errors are determined for the same indicated values that were obtained in that test.
3.3.4.3 The error of the accessory for each pair of indicated values is taken to be the difference obtained by subtracting the error determined in Sub-clause 3.3.4.2 from the error determined in Sub-clause 3.3.4.1. taking account of the signs of the errors (see Part 1, Sub-clause 2.7.1).
3.3.4.4 Instruments intended to be used with accessories of limited interchangeability may necessitate special values of certain circuit elements. Where this is necessary, the relevant information shall be given by the manufacturer and shall be complied with when carrying out the tests.
33.4.5 When an instrument cannot be tested without an accessory, the accuracy class applies to the combination only and the class index is marked on the instrument. The errors are determined in accordance with Sub-clause 3.3.4.1.
33.5 Non-interchangeable accessories The accessory is tested in combination with its own
instrument. There are no requirements relating to limits of error for either component alone and the class index relates to the combination.
4 Reference conditions and intrinsic
errors
4.1 Reference conditions See Part 1.
4.2 Limits of intrinsic error, fiducial value See Part 1.
4.2.1 Correspondence between intrinsic error and accuracy class
See Part I.
4.2.2 Fiducial value
The fiducial value for an interchangeable accessory or an accessory of limited interchangeability corresponds to the rated value.
The class index is marked using Symbol E- 1 given in Table 111-1 (see Part 1, Clause 8).
5 Nominal range of use and variations
5.1 Nominal range of use
See Part 1 and Table 11.8. 5.2 Limits of variations See Part 1.
5.2.1 and 5.2.2 See Part I. These sub-clauses apply when relevant (e.g. to reactor boxes).
5.2.3 This sub-clause of Part 1 does not apply to accessories.
5.2.4 See Part 1. However, this sub-clause does not apply to an accessory which is intended to be supported by its associated wiring or supported by a bus bar.
5.3 Conditions for the determination of variations
See Part 1.
6 Further electrical and mechanical requirements
6.1 Voltage tests, insulation tests and other safety requirements
See Part 1.
6.2 Damping
The requirements of Part 1 do not apply to accessories.
6.3 Self-heating
See Part 1.
6.4 Permissible overloads
6.4.1 Continuous overload
For the recommended test, see Part 9, Sub-clause 4.7.
Accessories, except those provided with a non-locking switch, shall be subjected to a continuous overload of 120 % of the rated value for a period of 2 h.
After having cooled to the reference temperature, the accessory shall comply with the requirements relating to its accuracy class.
This test shall be carried out under reference conditions.
6.4.2 Overloads of short duration
For the recommended tests, see Part 9. Sub-clause 4.5.
Accessories, except those provided with a non-locking switch, shall be subjected to overloads of short duration.
6.4.2.1 The currents and voltages for the overloads of short duration shall be the product of the relevant factor given in Table W-8 and the rated value of the shunt or the series resistor (impedance), unless other values are stated by the manufacturer.
6.4.2.2 The full duration of each overload shall be applied except when an automatic cut-out (fuse) fitted to the accessory has interrupted the circuit in less than the time specified in Table IV-8.
The automatic cut-out shall be reset (or the fuse replaced) before the application of the next overload.
6.4.2.3 After having been subjected to the overloads of short duration and after having cooled to the reference temperature, an accessory shall comply with the requirements relating to its class index; however, the overloads shall not be repeated.
6.5 Limiting values of temperature
See Part 1.
6.6 Deviation from zero
There are no requirements relating to deviation from zero for accessories.
7 Constructional requirements
7.1 Sealing to prevent access
See Part 1.
7.2 Scales
There are no requirements relating to scales for accessories.
7.3 Preferred values
7.3.1 The value of the resistance of a shunt should be such as to develop one of the voltage drops given in Sub-clause 7.3.2 for one of the preferred instrument currents given in Sub-clause 7.3.1 of the relevant part.
7.3.2 The voltage drop at the nominal current of a shunt should be one of the following values:
50 mV, GO mV, 75 mV, 100 mV, 300 mV.
7.4 Adjuster(s), mechanical andlor electrical There are no requirements relating to adjusters for accessories.
8 Information, general markings and
symbols
8.1 Information See Part 1.
8.1.1 A series resistor (impedance) shall be marked with its resistance (or impedance at a marked frequency) expressed in ohms and/or with its nominal current.
These values are treated as rated values and shall be stated as required by Item e) in Sub-clause 8.1 of Part 1.
8.2 and 8.3 See Part 1,
9 Markings and symbols for terminals See Part 1.
10 Tests to prove compliance with BS 89-8.
See Part 1.