Timers

Timers and Counters are devices that do what their name implies; they can be used to count events or signals external to the system, or they can be used to time activities. A counter/timer is a hardware device that must be initialized or programmed just as other I/O devices.

A timer is a device that counts down from a specified time interval and used to generate a time delay, for example, an hourglass is a timer. 

A counter is a device that stores (and sometimes displays) the number of times a particular event or process occurred, with respect to a clock signal.

This Device helps you perform event counting, time period and frequency measurements, quadrature encoder position measurements, pulse width measurements, pulse generations, and pulse train generations. 

You can use this module for applications such as retrigger able pulse generation, two-signal edge separation measurements, continuous buffered event counting, and continuous buffered pulse train measurements. The device can provide digital de bouncing filters, high-speed DMA transfers, and isolation. The Counter/Timer Device includes the NI-DAQmx driver and configuration utility that simplify configuration and measurements. NI-DAQmx supports NI programming environments as well as Python, ANSI C, C#.NET, and Math Works MATLAB® software.

Types Of Timers

Suppliers of digital timers offer meter, delay-on, delay-off, one-shot, recycle, and interval delay timers.

Timer meters, indicators, or totalizers are used in applications for display of elapsed process time or tracking running time of factory machinery.

Delay-on timers require a predetermined period of time to pass between when the timer receives its input signal and when the output is energized. At the end of the time delay, the contacts open or close. If the contact is normally open (NO), then the load energizes at the end of the time delay. If the contact is normally closed (NC), then the load de-energizes after the time delay. Removing power resets the time delay and output. This capability is also called on-delay, delay on make, delay-on operate, operate delay, pre-purge delay, and delay-on energization.

Delay-off timers start their timing functions when the power supply is interrupted. When the power is initially supplied, the output relay contacts react immediately. When the power supply is removed, the output relay contacts remain in the activated position and the time period starts. When the time has elapsed, the output relay contacts release. This capability is also called delay on release, delay on break, release delay, post-purge delay, and delay on de-energization.

One shot timers are designed so that when power is applied to the timer, the contacts change position immediately and remain changed for the set period of time after the timer has received power. After the set period of time has passed, the contacts return to their normal position. These devices are also called pulse formers.

Interval delay timers are the opposite of delay-on devices in that the relay is energized immediately upon application of the supply or closure of the switch input, and goes off at the end of the period. Interval delay is sometimes called delay pulse.

Recycle timers act so that the closing of the control switch starts the cycling function. The load continues to turn ON and OFF at regular time intervals as long as the control switch is closed. The cycling function stops when the control switch is open. This function is sometimes called a flasher (flicker), or pulse generator.

What is Digital Timers

Digital timers keep track of timing; to trigger an action, to start timing once triggered by an action, or both. Some products are programmable while others may be fixed at a set internal time and function. In addition to the number and type of functions, these devices differ in terms of time range settings.

Digital timers are more compact and also more complex than electro-mechanical timers. If feedback/output control functions are required (in terms of an alarm or another pre-programmed event), a digital timer is a better fit than an electro-mechanical timer. Each digital timer offers digital programmability. Some models have a choice of LED or LCD display. Some also operate as multifunction devices and others with long time ranges. These programmable timer solutions are available in many forms to meet many different needs: time indicators, reset timers, repeat cycle timers and multifunction timers. digital timer models can be more complex yet remain rugged and require minimal maintenance.

Timers Applications

Digital timers have both common consumer uses and large industrial uses. Timers are used in process control equipment to assist in process regulation, they are installed in industrial equipment to record its use and age, and they are used as consumer electronics for household use and recreational use.

Timer Glossary And Function 

Preset Time

The preset time is the control time set by setting a time-variable timer.

Operating Time

The operating time means the time which elapses between the addition of predetermined input to the power supply circuit and input circuit and the completion of operation for preset time.

Hold Time

It means the time which elapses between the completion of operation for preset time and the start of resetting.

Pause Time

It means the time elapses between the start of operation for preset time and the addition of input required again for the power supply circuit or input circuit. Timer does not perform normal function unless this pause time is set longer than the timer reset time.

Resetting

It means that the operation returns to the state before starting while the timer is in operation for preset time or after it completes the operation for preset time. Resetting during the operation for preset time is referred to as halfway resetting.

Reset Time

It means the time elapses between shut-off of input to the power supply circuit or input of reset signal and the completion of resetting.

Timer resetting function shares the reset of contact, reset of mechanical parts such as pointer etc., reset of parts in internal circuits such as capacitor etc., and the value at which all of these parts complete their resetting operation is regarded as reset time. If the timer is used for a pause time shorter than specified reset time, the operation time expires earlier than preset, unexpected instantaneous operation takes place or the operation is failed, thus making it impossible to expect the normal operation. Therefore, be sure to set the timer pause time longer than the specified reset time.

Minimum Power Application Time

It means the minimum time during which power must be supplied in order to operate the timer normally, in the case of power supply off-delay timer.

Fluctuation of Operating Time

It means the irregularity in operating time caused when the timer is set at specified time and the operation is repeated under the same conditions. It is also referred to as repetitive error.

Voltage Error

It means the difference between the operating time at the rated voltage and that within the allowable voltage range.

Temperature Error

It means the difference between the operating time at the temperature of 20°±2°C and that within the allowable temperature range.

Set Error

It means the difference between the set time and the time which actually elapses. It is also referred to as a setting error.

Pause Time Error

It means the difference between the operating time to a fixed pause time and the operating time to a pause time that varies.

The pause time characteristics are the main characteristics of CR timer (timer exploiting charge and discharge of capacitor C and resistance R).

If the oscillation count timer (timer which comprises an oscillation circuit composed of CR and quartz and is operated by a counting circuit inside IC or micro-computer which counts the reference signal) is used, the pause time error becomes almost negligible owing to its principles of operation. Accordingly, the description about these characteristics may be omitted for the oscillation count timer.

Vibration Resistance, Functional

Means such a vibration occurs in the range where the contact closed with that vibration during the use of the timer remains closed for the specified time (3 or 1 msec.) minimum.

Vibration Resistance, Destructive

Means such a vibration occurs in the range where no part is damaged with that vibration during the transportation or use of the timer.

Shock Resistance, Functional

Means such a shock as occurs in the range where the contact closed with that shock during the use of the timer remains closed for the specified time (1 ms) minimum.

Shock Resistance, Destructive

Means such a shock occurs in the range where no part is damaged with that shock during the transportation or use of the timer and the operation characteristics are maintained.

Mechanical Life

Means the durability that is achieved when the control output is performed in the no-load state.

Electrical Life

Means the durability that is achieved when the specified voltage and current loads are individually applied to the control output while being turned ON and OFF.

Generally, the life of the timer is represented by the number of times the control output is performed.

When a load is connected to the control output, the term "electrical life" is used.

When no load is connected to the control output, the term "mechanical life" is used.

The electrical life is shorter than the mechanical life, and becomes longer as the load decreases.

The life of the timer is made longer by connecting a relay or a similar part rather than directly switching a large load with the control output.

Rated Power Consumption

Means the power that is consumed when the rated operation voltage is applied to the power circuit.

(Rated power consumption = rated voltage × current consumption)

Rated Control Capacity

Means the reference value that is used to determine the performance of the switching part of the load.

This value is represented by the combination of voltage and current.

Contact Resistance

Means the combined resistance that consists of the contact resistance between contacts, and the conductor resistance of pins and contact springs.

Insulation Resistance

Means the resistance between a contact or a conductive pin like the pin to which the operation voltage is applied, and a dead pin or a non-conductive metallic part like the time case, the base, or a retaining screw; or the resistance between contacts.

Withstand Voltage

Means the limit value that does not cause breakdown when high voltage is applied for one minute to the same location as measured for insulation resistance.

The detectable leak current is normally 10 mA.

In special cases, however, it may be 1 or 3 mA.

Withstand Surge Voltage

Means the limit value that shows the durability against momentary abnormal voltage resulting from lightning or switching a conductive load.

The surge waveform is represented by the standard impulsive voltage waveform at ±(1.2×50)μs or ±(1×40)μs.

How digital timers Work

digital timer Basics

Although there are many different kinds of digital timers, quartz timers are fairly cheap, and so much more accurate than other systems, that they have become the standard. Quartz timers are inside microwaves, computers and many other devices.

Piezoelectric Quartz

Quartz crystal has a very useful property called piezoelectricity. When an electric current is applied to a quartz crystal, the crystal bends. When the crystal snaps back, it releases a little jolt of electricity. How quickly the quartz crystal bends back depends on its size and shape.

The Oscillator

At the heart of a digital timer is a very small, and precisely cut, quartz crystal designed to vibrate at a specific frequency. As the crystal repeatedly bends and snaps back up, it sets up an oscillating current--an electric current that increases and decreases in regular waves. Because the quartz crystal is precisely cut, the electronic current oscillates at a predictable speed.

Using the Oscillator

The digital timer circuit counts the pulses of the oscillator, and makes certain actions happen when there have been a certain number of pulses. For example, a timer circuit in a watch would count pulses until a second has passed, then send a signal to display the next second, and restart the count. Another part of the circuit could then count seconds until a minute has passed, and then increment the minute counter. Timers can also send signals to other devices. For example, a timer in a burglar alarm might give someone 20 seconds to deactivate the alarm after a key is inserted in the door lock before triggering the alarm system, and contacting the security company.

Where are digital timers used?

a circuit used in, for example, radar sets, television equipment, and telecommunication systems primarily for the purpose of ensuring that certain processes occur in conformity to certain time relationships.

Five Benefits of Using Digital LED Timers

If you need a timer for your home or office, then you have two main choices. You can go with an analog model or a digital unit with a light-emitting diode, or LED, display. The reality is that digital timers offer better performance and features than what is possible with an analog design. Here are five benefits of using digital LED timers.

Accuracy and Precision

A major benefit of using digital LED timers is accuracy. These timers often use quartz crystals in order to generate electrical pulses that are far more precise than inexpensive mechanical devices. The National Institute of Standards and Technology even has guidelines regulating that digital timers need to be accurate down to half of the least significant digit shown on the LED display. This accuracy can make a difference because you will always be able to rely on the timer.

Visibility

Another advantage of using an LED timer is visibility. The LED face is bright and lit up. This means that you will be able to see the display from across the room, in the dark or from any angle. This is not the case with many analog timers where the numbers are incredibly small. You also always get the exact numerical position in the countdown unlike analog timers where you often have to guess based on the position of a clock hand or arrow between numbers.

Compact and Durable

Most digital LED timers available today are compact and durable. The amount of space needed for the internal electronics is very small. Some digital timers can be the size of a credit card and not much wider. You can get ones that fit in the palm of your hand. This is not the case with analog timers where many large mechanical components need to be present inside of the unit. Digital timers are less obtrusive, more portable and will last for a longer time.

Simple and Fast Controls

Setting an analog timer can sometimes be a problem. You usually have to turn a dial or knob of some sort in order to physically move the settings on the device. This can lead to a number of issues especially as the parts wear down. Digital timers have simple and fast controls. You just hit a minute and hour button followed by start when you are ready. This lets you set the timer up fast without having to fumble with dials.

Some Have Multiple Timers

Integrated circuits and electronics allow some digital LED timers to accept multiple programs at the same time. This means that you can actually have two or three separate countdowns going all at the same time on the same device. The ability to set multiple countdowns on a single unit can make doing things like cooking or tracking your daily schedule much easier.