--- title: "ATM in hotel card reader failure" subject: "Instrumentation II" chapter: 6 key: "semester_5/instrumentation_ii:atm-hotel-problem" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/atm-hotel-problem site: BCT Engineering --- # ATM in hotel card reader failure Instrumentation II · Chapter 6: Grounding And Shielding - Asked in: 2070 Asar, 2+2 marks - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/atm-hotel-problem - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-6 ## Question A commercial bank has placed its ATM counter inside a 5-star hotel. Customers would walk through carpeted hallways to reach the ATM and insert their debit card into the machine to retrieve cash. However, the bank faced a disturbing problem: the electronics in the card reader circuitry was failing frequently causing an adverse effect to the bank's reputation. What could have caused the problem? Explain the measures to prevent this problem. ## Short answer Static electricity builds up on customers from walking on carpet; when they insert the card, electrostatic discharge (ESD) damages the card reader electronics. Prevent by grounding the card slot bezel, adding TVS protection, using anti-static floor mats, maintaining humidity, and providing a touch plate to discharge before contact. ## Answer #### Cause Customers walking on **carpet** build up static charge by the triboelectric effect (friction), especially in dry air-conditioned hallways, reaching several kV. When they touch the ATM or insert the card, the charge discharges through the card slot into the card-reader electronics. This **electrostatic discharge (ESD)** has a nanosecond rise time and amplitudes up to 10-20 kV. It breaks down the gate oxide of the ICs, damages the magnetic-head amplifier and causes latch-up, so the reader fails repeatedly. The discharge also couples through radiation into nearby circuits. #### Prevention - Put the ATM in a **grounded metal enclosure** and ground the card slot's metal bezel to chassis so the discharge goes to earth. - Add **ESD protection** on the reader's input lines: TVS diodes, series resistors, RC filters, ferrite beads. - Use an **anti-static carpet/mat** or conductive floor at the ATM entrance, and keep humidity at 40-60 percent. - Provide a **metal touch plate** or grounded handle that customers touch first, to discharge safely. - Keep traces short, use a ground plane under the reader's PCB and guard rings; separate the sensitive circuits from the slot. - Use ESD-tolerant ICs and test the design to the IEC 61000-4-2 standard. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What most likely caused the repeated card-reader failure? A. Lightning striking each time B. Overheating of the carpet C. Low supply frequency D. Electrostatic discharge from people charged by walking on carpet Answer: D. Triboelectric charging reaches several kV and discharges into the reader when touched. (Key point: Cause) 2. How does ESD damage the electronics? A. It slowly drains the battery B. It increases the humidity C. Nanosecond kV pulse breaks down IC gate oxide and can cause latch-up D. It reduces the data rate only Answer: C. The very fast, high-voltage pulse exceeds the ICs' oxide breakdown strength. (Key point: Damage mechanism) 3. Which measure sends the discharge safely to earth? A. An insulated plastic slot with no grounding B. A grounded metal enclosure and a grounded bezel at the card slot C. Higher-value series capacitors on power D. A dry hallway Answer: B. A grounded metal path diverts the discharge away from the electronics. (Key point: Preventing entry) 4. Which environmental or floor measure reduces static build-up? A. Anti-static carpet and 40-60 percent humidity B. Very dry air-conditioning C. Rubber-soled mats with no conduction D. Higher-friction synthetic carpet Answer: A. Conductive floors and moderate humidity reduce charge generation. (Key point: Environment control) ## Related in Instrumentation II - [8255A card at F3H with keyboard and display](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Appi-f3h-keyboard-display) — Instrumentation II, chapter 2 - [Reducing failure probability in milk scheme](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Amilk-scheme-failure) — Instrumentation II, chapter 7 ## Related in other subjects - [Network design for 3-star hotel](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Ahotel-network-design) — Computer Networks and Security, chapter 1 - [ATM withdrawal sequence diagram](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Aatm-withdrawal-sequence-diagram) — Object Oriented Analysis and Design, chapter 2 - [Septic tank and soak pits, hotel of 80](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aseptic-tank-hotel-80-users) — Sanitary Engineering, chapter 9 - [Why LV winding is placed near core](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Alv-winding-near-core) — Electric Machine Design, chapter 3