Voltcraft dhhm 230 operating hours timer voltcraft dhhm230 the voltcraft dhhm 230 operating hours timer is designed to din dimensions with an added countdown timer feature for installation in power supplies lab equipment and control panels it fits into a standard module with din dimensions 48 by 24mm and and the 6 display digits are 10mm high the unit can be configured with an alarm set to trigger an optional led or buzzer upon reaching a pre set value alternatively it can be set up as a