ITR (International Time Recording Co.) Master / Slave Clock System Modernization

This ITR Master and Slave Clock pair dates from the 1920s.

The Master Clock on the left is a precision regulator designed to keep time as accurately as practical during that era and within reasonable costs to be economically viable.

The timekeeping of the Slave Clock above was controlled by the Master Clock on the left using an electrical signal activated by contacts on the Master Clock and transmitted over wires to the Slave Clock. More details about the circuit and process are described on the next page.

These clocks were used in schools and businesses for the purpose of maintaining the same time on all clocks throughout the facility. One Master Clock could control all of the Slave Clocks on premises.

The goal of this project was to eliminate the requirement for the physical wires that were used to connect the clocks, and transmit the signal to advance the Slave Clock using WiFi. By replacing the wires with a modern communications protocol, the requirement for a physical connection was removed and the clocks' locations are no longer constrained to be in relatively close proximity. The clocks can be located anywhere in the world and remain synchronized as long as an Internet connection is available at each location.

It is important to note that these changes did not require any modifications to these antique clocks. The modernizing circuits were simply connected to the clocks' existing wire electrical connection points. The clocks remain in their original condition.