Elapsed time is the interval between a starting event and an ending event. An elapsed time meter (ETM) measures this interval with a readout in seconds, minutes, hours, or days. In an industrial application, 
an ETM can monitor accumulated run time, measure machine utilization, determine the need for scheduled maintenance, verify warranty status, or for any application where time-in-use or a cumulative time interval must be tracked. Elapsed time meters are sometimes called hour meters or run time accumulators. ETMs can be electronic or electro-mechanical. In some cases, the elapsed time function is part of a multi-function instrument.
Electronic ETMs
Low-cost electronic elapsed time meters are small, panel-mounted units with a 5 or 6-digit LCD display. Maximum reading is usually 99999 hours, which equals 11.4 years of continuous use. A typical product line is the ENM T1100 Series (upper left). These 6-digit LCD hour meters have a maximum reading of 99999.9 hours. A quartz crystal provides an accurate time base. Accumulated hours are stored in non-volatile memory that does not rely on a battery. They operate from 5-28VDC and can be reset by a remote contact closure. The 1¼”x2″ face comes in 3 bezel styles. The Lascar EMC1500 (lower left) has two ranges: 9999.9 and 99999 hours. It can be used to track total hours (non-resettable) or trip hours (resettable). This 0.8 x 1.75″ meter mounts in a single hole and operates from 5-27VDC. It generates a pulse output every hour. The ENM T1151 Series (right) are circular 6-digit LCD hour meters with the same performance as the T1100 series. These 2¼” diameter units operate from 8-28VDC. Similar models operate from AC mains to 250V.
ATS offers a variety of stand-alone digital meters with elapsed time capability. All have LED displays and operate off AC mains or a low-voltage AC/DC source. Run/Hold and Reset inputs are isolated from the power inputs. Most models have a digital communication option for network setup and interrogation. The STD-11 measures elapsed time to 10000 seconds. The STD-525T shows elapsed time in minutes and seconds, up to 100 minutes. The large AE Series meters have an option to display elapsed time as hours:minutes:seconds, for up to 100 hours. They can count up or count down, with 2″ to 8″ high digits. A rechargeable battery retains the count during power outages. ATS Day Counters show days since or days until an event in 2″ to 12″ high digits. The London Electronics Fusion series also offers elapsed time capability in days, hours, minutes, or seconds, with 2″ to 16″ high digits. Other Fusion features are similar to the AE/373.
Electromechanical ETMs
Electromechanical ETMs have a wheel-type indicator to store and display accumulated time in minutes or hours. An internal clock motor or clock movement is powered from either AC mains or a low-voltage source. Advantages of this meter type include simple two-wire connection and a readout that is visible even without power applied. The Weschler GH/BH models have a 6-digit hours or minutes display in a 2½” or 3½” size. Maximum reading is 99999.9. They operate from AC mains up to 480V. The manual reset version is shown here (upper left). The Weschler 240 (formerly Yokogawa) are also AC-powered units in 2½” or 3½” sizes. Reset and non-reset versions are available in 5 case styles, including the Big Look (upper right). The Simpson ETM line has 6 case styles. 3½” models (lower left) are AC mains powered. 1½” models are either AC or DC powered. All are non-resettable and have a 6-digit readout, except the 109ET, which has 7 digits. ENM’s electromechanical products include AC mains and low-voltage AC/DC models. They feature quartz-crystal accuracy and tamper-proof construction (no reset). Popular sizes are 1¼”x2″ rectangular and 2¼” round.
Multi-Function Meters
Some meters provide the elapsed time function as part of a multifunction instrument. Counters, timers, and clocks are typical products that may also monitor elapsed time. Here are a few examples (clockwise from left). The top display on the ENM T39 is a 6-digit LCD hour meter. The second display is a 6-digit event counter. ATC’s 5708A Timer-Counter is a 1/32 DIN meter with 23 functions, including a day/hour/min/sec elapsed time display to 8 digits. The Extech EA15 Thermocouple Datalogger records two temperature channels and includes a timer function that measures elapsed time. The N30O Counter from Sifam is a multifunction 1/8 DIN panel meter that can provide runtime tracking to 99999 hours. Four alarm outputs and Modbus communication are optional. The ENM PT33 combines a 6-digit hour meter with a battery voltage monitor and a 10-segment bar graph for charge level indication.
Electronic ETMs are sometimes called digital ETMs, and electromechanical ETMs are often called analog ETMs. Regardless of the terminology and technology, many solutions for measuring elapsed time in industrial applications exist. View Weschler’s lineup here.