scope:

This specification covers switchboard and portable electrical frequency meters for use in presenting visually the frequency of 60 or 400 cycle per second electric power system by a marked dial and pointer.

The type designation of meters shall be in the following form, and as specified (see 3.24 and 6.2):

Meters covered by this specification are designated by the two letter symbol "MR".

The style is designated by a two-digit number which signifies the following characteristics:

The first digit designates the normal size and shape of flange on switchboard meters, as follows:

4 - 4-½ inch, rectangular flange

6 - 6 inch, rectangular flange

The first digit designates the accuracy classification of portable meters, as follows:

1 - 1.5 percent

The second digit designates the type of mounting and the scale length in angular degrees, as follows:

8 - Flush mounting, 90 degree scale

9 - Flush mounting, 250 degree scale

The second digit designates the voltage rating, as follows:

1 - 115 volts

2 - 230 volts

8 - 115 and 230 volts

The color scheme of the dial background, markings and pointer is designated by a single letter, as follows:

B - Black dial background, white markings and pointer.

W - White dial background, black markings and pointer.

The center scale frequency shall be designated as follows:

60 - For meters designed for a center scale frequency of 60 cycles per second.

400 - For meters designed for a center scale frequency of 400 cycles per second.

The frequency range shall be designated by a single letter, as follows:

A - 59 to 61 cycles per second

B - 55 or 56 to 65 cycles per second

C - 390 to 410 cycles per second

D - 350 to 450 cycles per second

A single letter shall designate special features, as follows:

H - High-impact-shock resistant.

The type designation MR49W60AH signifies:

(a) MR - Electrical frequency meter.

(b) 49 - 4 ½ inch rectangular flange, switch-board meter, flush mounting, 250 degree scale.

(c) W - White dial background with black markings and black pointer.

(d) 60 - Center scale frequency of 60 cycles per second.

(e) A - Frequency range of 59 to 61 cycles per second.

(f) H - High-impact-shock resistant.

The type designation MR11W400 C signifies:

(a) MR - Electrical frequency meter.

(b) 11 - 1.5 percent accuracy class portable meter with voltage rating of 115 volts.

(c) W - White dial background with black markings and black pointer.

(d) 400 - Center scale frequency of 400 cycles per second.

(e) C - Frequency range of 390-410 cycles per second.

intended Use: