coulometer

https://doi.org/10.1351/goldbook.09157
Measuring instrument to obtain the electrical charge passed in an experiment, or to produce a known amount of substance in a titration.
Notes:
  1. The silver coulometer is a primary reference measurement procedure for charge and current. By weighing the mass of silver deposited in a known time at constant current, the charge and current are calculated from Faraday’s laws of electrolysis.
  2. Modern instruments for measuring trace water by Karl Fischer titration use the passage of a measured charge to produce iodine from iodide solution. They are known as Karl Fischer coulometers.
See: coulometric titration
Source:
PAC, 2020, 92, 641. 'Terminology of Electrochemical Methods of Analysis (IUPAC Recommendations 2019)' on page 682 (https://doi.org/10.1515/pac-2018-0109)