The Measuring Instruments (Gas Meters) Regulations 2006

Permissible effect of disturbances

14.—(1) Under rated operating conditions and in the presence of a disturbance, the performance requirements shall be as set out below.

(2) Where the relevant instrument, when constructed using electronic components, is intended to be used in a specified permanent continuous electromagnetic field the permitted performance during the radiated electromagnetic field-amplitude modulated test shall be within MPE.

(3) Electromagnetic immunity—

(a) The effect of an electromagnetic disturbance on a relevant instrument shall be such that—

(i) the change in the measurement result is no greater than the critical change value as defined in paragraph 14(3)(c); or

(ii) the indication of the measurement result is such that it cannot be interpreted as a valid result, such as a momentary variation that cannot be interpreted, memorised or transmitted as a measuring result.

(b) After undergoing a disturbance, the relevant instrument shall—

(i) recover to operate within MPE;

(ii) have all measurement functions safeguarded; and

(iii) allow recovery of all measurement data present just before the disturbance.

(c) The critical change value is the smaller of the two following values—

(i) the quantity corresponding to half of the magnitude of the MPE in the upper zone on the measured volume;

(ii) the quantity corresponding to the MPE on the quantity corresponding to one minute at maximum flowrate.

(4) Effect of upstream-downstream flow disturbances—

• Under installation conditions specified by the manufacturer, the effect of the flow disturbances shall not exceed one third of the MPE.