Electrostatic Sensors
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The SK Series electrostatic sensor measures static electricity and humidity at the same time. Because static electricity generation is closely related to humidity, the SK Series can determine the electric charge of the area around the target while understanding environmental conditions. Whereas conventional static electricity measuring instruments are prone to errors if the distance to the target changes, inline SK Series devices can correct static electricity measurements according to the target distance. Hand-held types are also available if measurement is needed at multiple points along a process. The SK Series’ various functions allow users to obtain a detailed, accurate understanding of the conditions in areas prone to static electricity problems.
Electrostatic sensors are measuring instruments designed for checking the amount of static electricity. Static electricity is measured through electrostatic induction, where a charged object becomes attracted to a nearby conductor. Non-contact measurement of static electricity is possible simply by pointing the sensor at the target.
The electrostatic sensor itself includes a sensor part that is pointed at the target and an amplifier that calculates and displays the signal obtained from the sensor. Hand-held type sensors include both of these parts in an integrated unit.
Sensor and amplifier
Hand-held type
Electrostatic sensor measurement principle
A sensing electrode in the electrostatic sensor is used to measure the electric field intensity of a charged target, which generates an inductive charge in the sensing electrode. This inductive charge creates a current that is converted into an AC voltage signal and the charged potential is then detected from this signal.
Measured values become smaller as the electrostatic sensor moves farther away from the target and larger as the sensor moves closer (distance-dependent measurement). Accurate measurement is possible if the target is larger than the detecting range but if the target is smaller the measured value is less than it actually is (target size-dependent measurement).
KEYENCE’s SK-050/1000 Series electrostatic sensors feature a distance correction function that automatically compensates for distance-related errors. Users can easily prevent measurement errors by entering the installation distance into the amplifier.
Benefits of Electrostatic Sensors
Static electricity intensity can vary depending on the location even within the same room. Individual parts can also have different charges. With a hand-held type static electricity sensor, pinpoint measurement is possible wherever accurate measurement of the static electricity amount is needed.
Even in a static-free room, parts can become charged through friction, peeling, or contact during assembly. Static electricity causes dust and particles to become attracted to and adhere to charged parts. If dirt adheres to parts sent to the next process, that dirt can end up inside the product.
Hand-held types can also be used to measure the amount of static electricity in an assembled part. If the charge exceeds the allowable amount the part will be prone to dust and dirt. Static eliminators (ionizers) or other devices must then be used to eliminate static electricity. In this way, hand-held electrostatic sensors can be used to prevent adhesion of dust, dirt, and other contaminants.
To ensure effective countermeasures against static electricity in a production line, accurate measurement of static electricity generated at various locations through friction, peeling, and contact is necessary. Such conditions for static electricity generation can occur at various points in the manufacturing process and using multiple electrostatic sensors enables measurement of static electricity in multiple locations.
By installing a large number of electrostatic sensors on the production line for measurement of generated static electricity at various locations, users can utilize both accurate control of static eliminators (ionizers) and accurate detection of the effects of static elimination. Continued measurement of static electricity and analysis of the accumulated data also make it possible to understand how static electricity amounts change due to changes in humidity and identify new areas where static electricity countermeasures are needed.
In other words, measuring static electricity at multiple locations along the production line allows users to prevent problems caused by static electricity in addition to checking the effectiveness of static eliminators and the status of current static electricity countermeasures.
There is an obvious close relationship between humidity and static electricity, but defining that relationship is difficult. Accurately determining this relationship is possible, however, with an electrostatic sensor capable of measuring humidity and static electricity at the same time.
Static electricity generation is less likely to occur if the relative humidity is 60% or more. However, because humidity changes as the temperature changes, the humidity may differ from place to place even in the same room. For example, the temperature around manufacturing equipment tends to be relatively high with low humidity. This means it is important to maintain an appropriate humidity where the measurement target is located rather than measuring the entire production area.
Using an electrostatic sensor to measure static electricity and humidity at the same time allows users to determine whether an area is likely to cause static electricity problems due to dry air. The data measured by the sensor can then be used to determine the most appropriate countermeasures against static electricity, such as by preventing targets from becoming charged or eliminating static electricity using a static eliminator (ionizer).
Electrostatic Sensor Case Studies
Food and medicine industries
A major static electricity problem that must be addressed in the food and medicine industries is “popping.” For example, when conveying tablets in a parts feeder, the guide rails can become charged through friction. If these tablets and a charged film repel each other, the tablets can pop out of their pockets. Such problems cannot be prevented using a vision system or other vision sensors, and any time a problem occurs, the production line must be stopped or the defective products must be removed, reducing the operating ratio.
Such problems can be prevented, however, by using an SK-050/1000 Series inline electrostatic sensor to measure static electricity during conveyance with parts feeders or other equipment. A static eliminator (ionizer) can then be used to remove static electricity if the measured values reach the upper limit.
Electrical equipment industry
Damage caused by electrostatic discharge (ESD) is a major concern in the electrical equipment industry. For example, if a worker (grounded with a wrist strap) lifts a PCB that has been sprayed with PCB cleaner during cell processing, electric discharge may occur between the worker and the PCB, causing damage to the mounted IC components. This is because the PCB became charged when sprayed with the PCB cleaner. Although grounding is a common countermeasure against static discharge, grounding has no effect on insulators.
To prevent discharge in such cases, the static electricity on the PCB can be measured using an SK-H Series hand-held electrostatic sensor, and if the components are charged, the charge can be removed using a static eliminator (ionizer). This makes it possible to increase the effectiveness of anti-static measures during cell processing and to improve yield rates.
Automotive industry
A major static electricity problem in the automotive industry is the adherence of dust and dirt. Automobile bumpers become electrically charged after molding, resulting in dust and other dirt adhering to the components while being transferred to the coating process. Static electricity causes these foreign particles to strongly adhere to the products, and an external force is required to remove them. Even particles removed with an air blower will become reattached. If the particles are not removed properly before paint is applied, the surface will become uneven or irregular.
To prevent this, the SK-050/1000 Series inline electrostatic sensor can be used to measure static electricity on the bumper after molding, and if the measured value exceeds the upper limit, a static eliminator (ionizer) can then be used to remove the static electricity. This will prevent dust and dirt from reattaching even after removal with an air blower. This will also prevent paint from becoming uneven due to static electricity.
Frequently Asked Questions About Electrostatic Sensors
Static electricity can lead to various problems including adhesion of dust and other foreign particles, conveyance problems, electrostatic discharge (ESD) damage, malfunctions in electronic devices and equipment, and coating/printing problems. Adhesion of foreign particles, for example, can result in defective products. Meanwhile, conveyance problems can lead to packaging defects and lower operating rates due to temporary stops, and electrostatic discharge can result in decreased yields or increased costs due to damage to electronic components.
Electrostatic sensors installed at locations where static electricity is generated can help prevent such problems through constant measurement of the static electricity in addition to static eliminators (ionizers) to eliminate any generated static. Electrostatic sensors can also be used for pinpoint measurement of parts and equipment off the production line, with static eliminators being used to efficiently control static electricity.
Electrostatic induction occurs in a conductor placed near electrically charged substances (dust or other foreign particles), causing the surface of the conductor to become electrically charged. This electrostatic induction and the static electricity of the foreign particles will create a force (Coulomb force) that causes them to adhere to other objects. The adhesion strength will vary depending on whether the object is a conductor or an insulator.
For example, the Coulomb force in insulators with a large surface area to mass ratio such as films and sheet materials is much greater than the weight of the object. The static electricity magnitude also varies greatly with humidity. Thus, to prevent adhesion of foreign particles due to static electricity, measuring both humidity and static electricity is essential.
Electrostatic discharge (ESD) results in damage when a charged electronic component comes into contact with a grounded conductor. As the charged electronic component comes into contact with the grounded conductor, a current is suddenly applied to the circuitry inside the component. This current causes the circuit wiring inside the component to melt, resulting in a short circuit or a break in the circuit.
Electrostatic discharge failures can be caused in a variety of ways, including discharges from workers with a static electricity charge (human-body model), discharges from metallic or conductive objects (machine model), and discharges by the device itself (charged-device model). Measurement of the static electricity of the source objects is necessary to prevent problems caused by these models.
Static electricity problems can differ in nature depending on the industry or process. We introduce typical static electricity problems in different industries and processes along with some actual cases of improvement made by introducing ionizers.
