ISO 19235:2015

Overview

ISO 19235:2015 - "Analogue quartz clocks - Timing accuracy" is an International Standard that defines the basic parameters, requirements, and test methods for the timing accuracy of analogue quartz table and wall clocks. It applies to quartz movements with an oscillator frequency of 32 768 Hz and a nominal supply of DC 1.5 V. The standard excludes clocks for special applications (aircraft, ships, vehicles, facilities), clocks built into other products, and radio‑synchronized clocks.

Key topics and requirements

• Mean instantaneous rate: After continuous running for 3 days, the mean instantaneous rate (average of three daily instantaneous rates) shall be within −1.0 s/d to +1.0 s/d.
• Voltage coefficient (C_U): Variation of instantaneous rate per volt; required to be within −1.0 to +1.0 s/(d·V). Measured by comparing rates at nominal DC 1.50 V and at 1.35 V (90%).
• Temperature coefficients (C_t1, C_t2): Defined for decrease (23 °C → 8 °C) and increase (23 °C → 38 °C). One coefficient must lie between 0 and +0.1 s/(d·°C) and the other between −0.1 and 0 s/(d·°C).
• Test conditions and apparatus:
  • Ambient: 18–25 °C, variation ±2 °C; relative humidity 50–70%.
  • Power supply: nominal DC 1.5 V.
  • Pre‑running: at least 2 h in test environment.
  • Apparatus resolution and permissible errors are specified (instantaneous rate instrument resolution 0.01 s/d, max error ±0.03 s/d).
• Performance over temperature and ageing:
  • Instantaneous rate in 8–38 °C should be within −2.0 s/d to +1.0 s/d.
  • Typical ageing effect: about ±0.2 s/d per year under normal use (informative guidance).

Applications and users

ISO 19235:2015 is practical for:

• Manufacturers of analogue quartz table and wall clocks for design verification and production quality control.
• Test laboratories and conformity assessment bodies performing timing accuracy tests.
• Product managers and spec writers preparing technical specifications or datasheets for quartz clock movements.
• Procurement and quality assurance teams requiring objective acceptance criteria for timing performance.
• Retailers and consumer information to set realistic performance expectations.

This standard supports consistent, comparable benchmarking of timing accuracy and helps reduce warranty claims and field failures related to timing drift.

Related standards

• ISO 6426-2 - Horological vocabulary (technical and commercial definitions) - referenced by ISO 19235.
• ISO/TC 114 (Horology) - technical committee responsible for related clock and watch standards.

Keywords: ISO 19235:2015, analogue quartz clocks, timing accuracy, quartz clock testing, mean instantaneous rate, voltage coefficient, temperature coefficient, horology standard.