Stopwatches and Timers

Stopwatches and timers are instruments used to measure the time elapsed between two events. As opposed to the conventional clock, which displays the current time in hours, minutes, and seconds from an absolute starting point (often from the beginning of a day), stopwatches and timers simply measure and display the time elapsed from a relative point in time, starting from the instance of switching them on. The difference between a stopwatch and a timer is that timers are integrated into electronic systems to trigger events at a pre-set condition. In contrast, stopwatches are timers with a manual interface to record and measure elapsed time of an event counting upwards from zero.

 

Timer Selection:

 

Timers are selected based on the application and the accuracy required for a measurement. The accuracy of a timer is denoted by its Least Count (LC) and Resolution (R). The least count is the smallest value that a timer can measure, generally in the order of 0.001s (milliseconds) for industrial applications. Resolution is the smallest incremental change indicated by the timer. Industrial stopwatches and timers are often limited to millisecond (ms) LC with a resolution of 0.001 s or higher. More sophisticated aerospace and military applications have timers with finer LCs and resolutions (in the order of microseconds ors).

 

Timer Types and Applications:

 

Depending on the operating principle, timers are classified as Mechanical, Electro-Mechanical, and Electrical. A Mechanical timer uses the conventional spring mechanism set by manual turning of a dial to the time interval desired. Energy stored in the mainspring during turning causes a balance wheel to rotate back and forth. For every wheel swing, the gear train is released to move forward by an incremental fixed amount, causing the dial to move back until it reaches zero steadily. At zero, the lever arm strikes a bell. Hourglass is a classic example of mechanical timers.

 

Electro-Mechanical timers use the bimetallic thermal expansion principle to operate. Electric current is flown through a bimetallic strip made with two metals of different linear thermal expansion. Electrical resistance causes heat generation and thermal expansion. The expanded metal move towards the electrical switch contact and generates a time signal. The most common application of the Electro-Mechanical timer is the “flasher” unit installed in automobiles to flash turn signals. Advanced electro-mechanical timers use miniature synchronous AC motors to drive a cam against a comb of switch contacts. AC power is accurately regulated to turn the cam. These timers are standard in household washers, driers, and microwave ovens. Though these timers are robust and less expensive, Electrical timers have replaced Electromechanical timers because of high precision and minimal moving parts.

 

Electronic timers operate on digital logic and are inexpensive compared to many mechanical and electromechanical timers. Development of IC (integrated circuits) and Controllers lead their easier integration to automation systems. Modern controllers use PLCs (Programmable logic controllers) to integrate process control equipment such as pressure switches and flow switches to automate industrial motors and pumps.

 

Electronic Timer Functions:

 

Electronic timers are control devices that output a signal at a preset interval after an input signal is received. An electronic timer does four essential functions: Power supply (supply a pre-defined voltage to internal components), Input function (receives a signal from input devices and outputs the signal to timing section), Timing function (measures the time and outputs a signal to the output section at a specified time), and Output function (outputs signal to output devices).

 

Timer Operating Modes:

 

Most Electronic timers operate in four modes. The operating mode is selected based on the type of application:

  1. ON-delay Operation: Output signal switches on the device or system at a predefined time. Application: Delayed traffic signal changes from red to green after the push button is pressed.
  2. OFF-delay Operation: Output signal switches off the device or system at a predefined time. Application: Internal lights of a passenger car remain lit for several seconds after opening and closing the doors.
  3. Flicker Operation: repeatedly turns ON and OFF at the set time after an input is received. Application – Fountain water released and held at one-minute intervals.
  4. Interval Operation: the output turns ON simultaneously as input, and the output turns OFF after a set time. Application – A toy horse operates for five minutes when $1 is inserted.

 

Timer Calibration – Why is it essential:

 

Following errors are set into a timer due to prolonged usage at various operating conditions. Operators should measure and eliminated these errors using calibration and resetting:

  1. Operating time difference error: Inaccuracies are observed when the timer repeats operation under the same conditions with a specified set time.
  2. Setting error: This is the time difference between the operating time of the timer and the actual time.
  3. Total Error (or Time Switch error): Combination of setting error, operating time accuracy, Influence of external factors such as voltage and temperature
  4. Cyclic Error (Errors generated every month): Cumulative errors in the internal clock set every month, due to variable operating loads.

 

Cumulative Timer errors often result in operational uncertainties leading to maintenance loss. Calibration avoids these errors, ensures timers’ accuracy for sustained and repeated use, and enhances service life. Following a regular and timely calibration schedule ensures accuracy of measurement and enhances process accuracy.

 

e2b calibration offers industry-leading ISO-certified timer & stopwatch calibration services. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to test and calibrate your timers. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.

 

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