One: What is the function of the ground monitor
A1: The grounding monitor can monitor whether the following are qualified:
1) Whether the resistance value of the human body through the wrist strap is qualified
2) Whether the human body is charged (contact or induced AC or DC current, static electricity generated by itself)
3) Whether the ground resistance of the table is qualified
4) Whether the grounding resistance/impedance of the equipment or tool is qualified
5) Is there electromagnetic interference (EMI) in the equipment or tools and the grounding point?
6) Are the devices being processed (such as circuit boards) subject to AC/DC overload voltage or electrostatic hazards generated by equipment, tools, and human bodies (EOS/ESD)
Two: Why monitor human body potential?
A2: The human body may be charged due to the following reasons:
1) The body's own static electricity
2) Contact with unqualified grounding or leakage power tools or equipment
3) Induction charging
The extra voltage carried by the human body acts on electronic devices to form electrical overload (EOS), which can cause product damage. Therefore, while monitoring whether the earth resistance of the human body is qualified, it is also necessary to monitor whether the human body is charged.
Three: Why should we distinguish resistance and impedance?
A3: The ability to prevent charge movement is called resistance or impedance. For direct current, there is only the concept of resistance; for alternating current, not only the resistance has the ability to prevent the movement of charge, but the capacitance and inductance can also prevent the movement of charge, so impedance refers to the vector sum of resistance, capacitive reactance, and inductive reactance. It is more meaningful to test impedance for AC equipment or tools. Ohm's law applies to both resistance and impedance, in ohms (Ω).
Four: Why monitor electromagnetic interference (EMI)?
A4: The electromagnetic radiation of the equipment and tool itself will produce electromagnetic interference, and the ground point may also have electromagnetic interference conducted by other equipment. These electromagnetic interference have the potential risk of electrical overload (EOS), so it is necessary to monitor whether the equipment and ground point exist EMI.
Five: The technical principle of monitoring single-line wrist strap?
A5: When the human body is grounded through a single-line wrist strap, a test loop cannot be formed, and monitoring can only be achieved by the following methods:
1) Capacitance method: Use the capacitance between the human body and the earth to estimate the equivalent resistance between the human body and the earth, in order to assess whether the human body is grounded.
2) Waveform distortion analysis method: apply a test signal to the wrist strap jack to monitor whether the sinusoidal waveform of the signal is distorted, so as to assess whether the human grounding circuit is complete and obtain the equivalent grounding impedance. This technology is a proprietary technology unique to DESCO in the United States. It can 100% continuously monitor whether the human body grounding is qualified, and will not cause the trouble of false alarms.
Six: The technical principle of monitoring the two-wire wrist strap?
A6: When the human body is grounded through the two-wire wrist strap, a loop can be formed from one line of the wrist strap through the skin to another line, so a specific voltage can be used to measure the specific resistance to determine whether the human ground resistance is in Within the qualified range.
Seven: How to implement a true continuity test on a two-wire wristband?
A7: When the human body is grounded with a two-wire wrist strap, the resistance of the loop can be tested with a voltage. This creates the following problems:
1) The application of voltage for a long time will burn the skin and can only be tested intermittently. This is not a real continuous test. Usually the test time only accounts for 20% or less of the total time.
2) For highly sensitive electronic devices, the test voltage itself causes an electrical overload (EOS) effect on the device
US DESCO's grounding monitor uses an ultra-low test voltage, which can continue to act on the skin for true continuous testing without harming the skin. At the same time, the ultra-low test voltage will not cause EOS damage.
Eight: Why monitor the electrical overload (EOS) of the device (circuit board) being processed?
A8: When processing sensitive components or circuit boards, the equipment and tools may be unqualified for grounding or electrical leakage may cause electrical overload to the device. Unqualified grounding of the human body or induction charging may also generate static electricity. These electrical overloads have potential risks, so monitor the processed devices for EOS.
Nine: How to calibrate the real-time grounding monitor?
A9: Once the real-time grounding monitor is installed, it is inconvenient to remove the instrument and send it to a third-party calibration agency. When there are multiple instruments, it is not practical to send a third-party to perform calibration one by one. It is recommended to purchase the original standard resistance box. Just calibrate the standard resistance box first, and then calibrate each real-time grounding monitor on site with a qualified standard resistance box. This is a simple and efficient calibration method.