At this point in our blog series concerning ESD Awareness, we should consider some basic physics:
Ohm’s law is an extremely useful equation in the field of electrical/electronic engineering because it describes how voltage, current, and resistance are interrelated.
Ohm’s law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (.i.e. voltage drop or voltage) across two points, and inversely proportional to the resistance between them.
Resistance determines how much current will flow through a component. A very high resistance allows a small
amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.
An analogy to help understand these terms better is a water hose. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the hose size. For example, you can spray the water further away by increasing the water pressure and consequently the flow rate of the water. There is a direct relationship between pressure, flow and the hose diameter.
In a similar way, voltage, current and resistance are related to each other by the electrical engineering formula Ohm’s law.
Resistance to ground (Rtg) is a measurement that indicates the capability of an item to conduct an electrical charge (current flow) to an attached ground connection. For ESD control purposes, devices with a Rtg of less 1.0 x 106 are known as conductors (foam, floor mats) and must be connected to ground. ESD Control devices with an Rtg of 1.0 x 106 to < 1.0 x 109 are a special class of conductor, called dissipative (worksurface mats, gloves, smocks) and must also be grounded. The dissipative range of conductors is especially important for ESD control because it “slows down” a static discharge event. Devices with an Rtg of 1.0 x 1011 or greater are known as insulators. Insulators cannot be grounded and must be removed from the ESD Protected Area or neutralized with ionization.
The measurement may be shown in various ways. Most commonly:
- 1 kilohm
- 1 x 103 ohm
- 10^3 ohm
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This is the fourth in a series of blogs concerning the Basics of ESD. Be sure to sign up for our blog to follow the series.