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Q: What is an optical turnstile?

A: An optical turnstile is a security industry term for a pedestrian monitoring and control system that uses a card access system, infrared sensors and an intelligent control unit to detect and count persons walking through a lane or passageway.

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Q: How does an optical turnstile work?

A: Most large amusement parks, stadiums, subway systems use physical turnstiles to make sure that only one person enters for each token, payment or authorization presented. A metal bar is locked into a blocking position to prevent someone from walking through the passageway. When authorization is granted the bar is released and one person can walk through. The bar is re-locked after a person walks through the passageway.

An optical turnstile uses a card access system to determine when authorization is granted, and infrared sensors to detect a person walking through the passageway. No physical barrier is present. If a person walks through the passageway without authorization, then an alarm is generated. A sounder is activated, the card access system is sent an alarm signal, and a guard should respond to the alarm.

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Q: Where are optical turnstiles used?

A: Many office buildings, factories, banks, and other businesses already use some type of security system to protect their employees, clients, and assets. Security measures often include some type of identification card. The ID card is shown to a guard when entering a secured area or building. The guard is supposed to make sure that everyone entering the secured area has a valid ID card.

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Q: If there is a guard, why use an optical turnstile?

A: If a large number of people have to check with a guard or guards during a brief time frame (such as shift change), the probability of an unauthorized person walking past the guard without being checked increases. The combination of a guard and a set of optical turnstiles significantly reduces the chances of unauthorized entry into a secured area. The card access system checks the ID cards for validity, the optical turnstile ensures that only authorized persons enter the secured area, and the guard responds to alarms. The guard's workload is reduced from ID verification plus security enforcement to security enforcement alone.

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Q: If the guard's workload is reduced, does that mean saving money?

A: Yes. The reduced workload means that 1 guard with a set of lanes can provide the same level of security as 3 to 6 guards stationed at the entry to a secured area. The cost of hiring a guard ranges from approximately $28K to $60K per year depending on the area of the country, taxes, and benefits.

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Q: Are there other reasons to use optical turnstiles?

A: Some facilities use physical barriers such as turnstiles, and interlocking door systems or mantraps to control access into secured areas, preventing unauthorized persons from entering.

Aesthetic concerns often discourage the use of physical barriers at main entry points to secured buildings. The main lobby of an ornate office building is not a likely place for a physical turnstile, even though access control measures are necessary.

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Q: What kinds of optical turnstiles exist?

A: Optical turnstile housings come in a variety of sizes, and materials. The available sizes include a very small doorway mounted sensing package, a 4" x 8" x 38" housing, and intermediate sizes up to 8" x 60" x 38". Housings can be made from stainless steel, wood frame with laminate sides, synthetic Corian, granite, polished brass, and other exotic materials.

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Q: How do I decide what type of optical turnstile to use?

A: The location of the lanes is an important consideration. If the optical turnstiles are to be located in the front lobby of a prominent business, then selecting materials and colors that complement the building's interior design becomes important. Parking garage entryways are not usually as ornate as front lobby's and many times there is limited space.

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Q: How do I determine how many optical turnstiles should be used?

A: The first consideration is the number of people that will be using the lanes. Also, will they be all entering and leaving within a short time frame, or will they be spread out over several hours. Optical turnstile systems working with very fast card access systems and well trained people can operate as fast as one person every 2 seconds, or 30 people per minute.  However, ergonomic placement of card readers, card access system response time, and normal people movement issues can reduce the throughput to a more realistic 1 person every 3 to 4 seconds, or about 15 to 20 people per minute.

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Q: Is there a formula to calculate the number of optical turnstiles needed?

A: An exact formula is not practical, but to get a general idea of how many lanes will be needed, put the following equation into a spreadsheet. Vary the number of people and the number of minutes of high use to get an idea of the load on the turnstiles.

  • P = number of authorized people using the turnstiles in high use times

  • T = duration of time (in minutes) that the turnstiles will be in high use

  • R = rate of throughput (number of people passing through the turnstile each minute)

Note: Rate of throughput (R): 30 maximum, 15 realistic. R can be reduced to eliminate traffic jams at the turnstiles. 

(P / T) / R = number of lanes needed (round up any fractions to the next whole number)

A company has 5000 employees. This company operates from 7 to 5 Monday through Friday, the employees all come to work between 7 AM and 8 AM, and they all leave between 4 PM and 5 PM.

5000 people enter in 2 hours, so P = 5000, T = 120 (minutes), R = 15
(5000 / 120) / 15 = 2.77

This company will need at least 3 turnstiles to accommodate the 5000 employees. This formula requires a constant rate of 41.6 people entering per minute for the entire 2 hours, that constant entry rate is not realistic. People will probably come in groups, so the actual rate per minute could jump as high as 75 - 100 people. More turnstiles would insure that no traffic jams occur during peak entry times.

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Q: Are there differences between the shorter compact optical turnstiles and the longer optical turnstiles?

A: Yes. The differences range from card reader type and mounting, pedestrian throughput, aesthetic considerations and cost.

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Q: Does card reader type make a difference?

A: Three different types of card readers are available, the older insert reader, swipe reader, and the newest and easiest to use proximity readers. Any existing card reader systems in a building will have a very large affect in the decision of which reader to use.

Anybody who has used a bank cash machine has used an insert reader. You have to insert the card into the reader then pull it out. In order to do that you must be completely stopped. When an insert reader is used on an optical turnstile, it should be mounted on the end of the housing so it would be ergonomically easier for the user to insert and remove their card. The fact that a person must stop to use the insert reader inherently slows down pedestrian throughput. Some confusion can result when several lanes are set up next to each other. A reader mounted on a housing in the middle of several lanes might be used with the right hand or the left hand, and a person could accidentally walk through the wrong lane.

The swipe reader is used on many credit card point-of-sale cash registers. The card is swiped through a small slot, and the card is read. When a swipe reader is used on an optical turnstile, it can be mounted on either the top or side of the housing. Top mounting is ergonomically easier to swipe a card while passing though the lane, but the lane confusion described above is possible. Side mounting is slightly more difficult to swipe the card, however there is no confusion as to which lane is associated with the reader.

Proximity readers use a low power radio frequency to read cards. No physical contact is required, and that makes it very easy for a person to use. Some proximity readers have extended read ranges in excess of 12 inches. Proximity readers may be mounted at all three locations on the lane housing, end, top and side. The end and top mounting locations are subject to the lane use confusion described above. Another consideration with proximity readers is that the read range is reduced dramatically when they are mounted on metal surfaces, whereas the insert and swipe readers are not affected by the mounting surface.

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Q: Why do the longer turnstiles have a higher throughput than the compact turnstiles?

A: Longer optical turnstiles (48" - 60" in length) have a higher realistic throughput capability than the compact turnstiles (8" - 18").

The fastest card access systems on the market currently have a - second time delay from when the card is presented to when an access granted relay contact is generated. Some card access systems have as much as a 1-second delay.

A person using a longer turnstile can present their card to a proximity card reader, pause slightly in their stride, keep moving and by the time they reach the sensing area, the card has been verified access granted. The turnstile is immediately ready for the next person. The entire sequence happens in about 2 seconds or less.

If the same person using the same proximity reader were using a compact turnstile, they would be in the sensing area before the card access system could respond and grant access. An alarm would occur and the turnstile throughput would be stopped at that point. To prevent that alarm, the person would have to stop entirely at the entry side of the lane and wait for the access granted signal, then walk through the sensing area. That sequence could take slightly longer than 2 seconds, perhaps as long as 3 to 4 seconds, all due to the required stop the person must make to present their card and wait for the access granted signal.

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