Continuous or Constant Monitors pay for themselves improving quality, productivity, eliminating wrist strap daily testing and test result logging. “The wrist strap system should be tested daily to ensure proper electrical value. … Daily testing may be omitted if constant monitoring is used.” [Wrist Strap standard ANSI/ESD S1.1-2006 Annex A, 3 Frequency of Functional Testing]
Companies manufacturing products containing ESD sensitive items need to ask themselves “how important is the reliability of their products”? “Wrist straps should be tested periodically. The frequency of testing, however, is driven by the amount of risk exposure that can occur between tests. For example, what is the quantity of product handled between test periods? Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system. Typical test programs recommend that wrist straps that are used daily should be tested daily. However, if the products that are being produced are of such value that knowledge of a continuous, reliable ground is needed, and then continuous monitoring should be considered or even required.” [ESD Handbook ESD TR20.20-2008 Wrist Strap section 5.3.2.4.4 Test Frequency]
Per ESD Association ESD Handbook ESD TR20.20 Wrist Strap section 5.3.91 “Even if the wrist strap is working properly, a bad or intermittent ground connection will render the wrist strap system less than 100% effective.”
“If used correctly, a wrist strap checker will find faulty connections or system parts at the time of testing. However, it must be recognized that use of a wrist strap’ checker is only periodic. Also, if personnel adjust the wrist strap artificially by sliding the wristband up their arm or pulling it tight during the test just to’ get a -pass indication, the test must be viewed as faulty. Should the wrist strap system fail between checks an ungrounded or improperly grounded operator can potentially expose products to high human body voltages. … Wrist straps are stressed and flexed to their limits at a workstation. While a wrist strap is being checked, it is not stressed, as it would be under working conditions. Opens in the wire at the coiled cord’s strain relief are sometimes only detected under stress.” [ESD Handbook ESD TR20.20-2008 Continuous Monitor section 5.3.9.1 Introduction]
The ESD Association produced the ESD TR 12-01 technical report which is entitled “Survey of Constant (Continuous) Monitors for Wrist Straps” which includes: “Since people are one of the greatest sources of static electricity and ESD, proper grounding is paramount. One of the most common ways to ground people is with a wrist strap. Ensuring that wrist straps are functional and are connected to people and ground is a continuous task.” “While effective at the time of testing, wrist strap checker use is periodic. The failure of a wrist strap between checks may expose products to damage from electrostatic charge. If the wrist strap system is checked at the beginning of a shift and subsequently fails, then an entire shift’s work could be suspect.”
“Some continuous monitors can monitor worksurface ground connections. A test signal is passed through the worksurface and ground connections. Discontinuity or over limit resistance changes cause the monitor to alarm. Worksurface monitors test the electrical connection between the monitor, the worksurface, and the ground point.” [ESD Handbook ESD TR20.20-2008 section 5.3.9.3.1 Worksurface Ground Monitoring]
“Continuous monitors evolved as a means to evaluate the performance of wrist straps on a continuous basis” particularly in high value and high-risk operations (e.g., military and medical electronics were among the first major users). … The use of continuous monitors in conventional electronics manufacturing has increased in recent years as manufacturers have had the desire to increase reliability, customer satisfaction and company image.” [ESD Handbook ESD TR20.20-2008 Continuous Monitor section 5.3.9.1 Introduction]
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