Moving-coil mechanism (analog meter movement)

01

Pick the movement type and suspension

Simpson's Century analog panel meters use self-shielding permanent-magnet movements for DC ranges — annular, or a small-core magnet on the 1½-inch model 2121 — so calibration is unaffected by mounting in a magnetic panel; AC ammeters and voltmeters use magnetically damped iron-vane movements instead. The coil is carried on pivot-and-jewel suspension, or on a taut band in the T models. [1]

Suspension sets repeatability: Simpson lists 2% for pivot-and-jewel and 0.5% for taut-band movements, and offers taut-band DC microammeters from 0–10 µA (about 4,900 Ω) to 0–200 µA (about 234 Ω). [1]

For longer scales, Simpson's 250° long-scale meters more than double the scale length of standard movements, using a self-shielded permanent-magnet movement on pivot and jewel for DC and a rectifier-type movement for AC. [2]

Give the supplier the measured quantity (DC current, DC voltage, AC via rectifier or iron vane, frequency, speed via tachogenerator), full-scale range, coil resistance or input impedance, movement type and suspension, accuracy class, scale arc and length, dial markings, case style and size, mounting panel material, operating temperature and quantity.

02

Check full-scale current, accuracy, scale and overload

Simpson's Century DC microammeters run from 0–50 µA with about 1,800 Ω coil resistance to 0–500 µA with about 90 Ω, with resistance held to ±15% of the stated impedance, tracking of ±3%, 1.5 s maximum response, overload of 10× full scale for 1 s and 1.5× continuously, and operation from −20 to +65 °C. Scale lengths run from 31.7 mm on a 1½-inch meter to 103.9 mm on a 4½-inch meter, and net weights from 0.06 to 0.31 kg. [1]

The 250° long-scale meters list accuracy of ±2% of full scale for DC and ±3% for AC, the same response and overload ratings, 2% repeatability, and scale lengths of 121.16 mm (3½-inch) and 166.0 mm (4½-inch). [2]

Editorial calculation: a 0–50 µA movement of 1,800 Ω drops 50 µA × 1,800 Ω = 90 mV at full scale; to read 0–10 V it needs a series resistor of 10 V ÷ 50 µA − 1,800 Ω = 198,200 Ω, and ±2% of full scale on that meter is ±0.2 V. [1] [2]

An IEC-market data sheet states the same quantities by class. Rishabh's data sheet for its PQ moving-coil DC meters (48, 72, 96 and 144 mm square cases) gives accuracy class 1.5 to IEC 51 / DIN EN 60051 at 23 ± 2 °C (class 2.5 or 5 on the lowest microamp ranges), a 0–90° linear scale with lengths of 41, 61, 97 and 146 mm, and a movement on hardened pivots between spring-loaded sapphire jewels, eddy-current damped in the coil former. Overload is 1.2× rated continuously; voltmeters take 2× for 5 s once or 0.5 s nine times, ammeters 10×. Voltmeters run at 1 kΩ/V on the standard ranges, ammeters for external shunts are offered at 60, 75 and 150 mV, and the case is IP52 (terminals IP20 with back cover). Operating range is −5 to +50 °C, storage −40 to +70 °C, with 15 g / 11 ms shock and 10–55 Hz, 0.15 mm vibration ratings. [3]

Editorial calculation: a 100 A ammeter on a 75 mV external shunt needs a 0.75 mΩ shunt (0.075 V ÷ 100 A) that dissipates 7.5 W at full scale; and at 1 kΩ/V a 250 V voltmeter draws 1 mA (250 V ÷ 250 kΩ), twenty times the full-scale current of Simpson's 0–50 µA Century movement. [3] [1]

03

Read the accuracy class against the current IEC 60051 editions

IEC 60051 is the series behind the accuracy classes on analogue panel meters. Part 1 "specifies definitions and general requirements for direct acting indicating analogue electrical measuring instruments and their accessories"; its sixth edition was published on 3 February 2016, replacing the 1997 fifth edition. Part 2 applies to direct acting indicating ammeters and voltmeters with an analogue display, including those whose scale marks do not correspond directly to the input quantity and those with electronic devices in their measuring or auxiliary circuits; its fifth edition, published on 30 August 2018, replaced the 1984 fourth edition and is used together with IEC 60051-1:2016. [4]

Rishabh's PQ data sheet states accuracy class 1.5 "to IEC 51 / DIN EN 60051" at 23 ± 2 °C [3], and Simpson gives tracking of ±3% and repeatability of 2% or 0.5% by suspension [1]. The class number and the tracking or repeatability figures come from different conventions, so ask each supplier which part and edition of IEC 60051 the class was tested to, at which reference temperature, and whether the meter has electronic circuits that bring it under the added scope of the 2018 Part 2.

For meters whose scale reads a converted quantity, such as a tachometer indicator calibrated in rpm from a current input, the 2018 Part 2 applies "provided that the relationship between them is known" [4]. Give the supplier the input-to-scale relationship and the required class so the scale and calibration can be checked.

Editorial calculation: on a class 1.5 meter with a 100 µA range, a reading may differ by about ±1.5 µA from the true value if the class is defined as a percentage of full scale; the 2016 Part 1 replaced an edition 18 years older and the 2018 Part 2 one 34 years older. [4] [3]

Values are from the Standard Norge catalogue pages for IEC 60051-1 (1997, 2016) and IEC 60051-2 (2018); the class definitions in the full standards were not reviewed.

04

Compare what suppliers offer

No manufacturer record has been reviewed for this product yet. Send your specification and CNFX will match it against manufacturer records.

Ask each supplier for movement type, suspension, full-scale current and coil resistance with tolerance, accuracy, tracking, repeatability, overload and temperature ratings. [1] [2]

05

Trace what each part controls

This is a functional reference built from the sources cited; it is not a full specification.

06

Fill the specification fields with values for your design

A moving-coil mechanism quotation needs values for your design. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the signal, accuracy and dial data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Quantity measured: [DC A; DC V; AC; speed]
Range: [full scale]
Movement: [moving coil; iron vane; rectifier]
Suspension: [pivot and jewel; taut band]
Accuracy: [±% F.S.]
Scale: [arc °; length mm; dial]
Case/size: [inch; material]
Quantity: [units]

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