What type of Ioniser to choose
Last week we learned the difference between conductors & insulators. We went on to explain what ionisers are and when you need them in your EPA. As promised, today we’ll be looking at the different types of ionisers available.
What is an Ioniser?
But first a quick recap of what an ioniser is: An ioniser creates great numbers of positively and negatively charged ions. Fans help the ions flow over the work area. Ionisation can neutralise static charges on an insulator in a matter of seconds, thereby reducing their potential to cause ESD damage.
Types of Ionisers
Electrical ionisers generate air ions by a process known as corona discharge. A high voltage is applied to one or more sharp points and quantities of air ions are created. Fans or blowers may be incorporated in the ioniser to assist the movement of the ions and enhance performance.
- AC Ionisers
AC Ionisers use a transformer to multiply the AC power line voltage. AC stands for Alternating Current, which means that the power cycles from positive to negative sixty times per second. The AC ioniser therefore produces both positive and negative ions from the same points or emitters. The drawback with this approach is that many ions recombine because the cycle frequency is too fast. For this reason, most AC ionisers rely on fans or blowers to be effective.
- Pulsed DC Ionisers
Pulsed DC ionisers utilise separate power supplies to generate positive and negative voltages and usually each power supply has it’s own dedicated emitters. The power supply alternates between positive and negative, but usually at a lower frequency than AC units. In this way, ion recombination is reduced and performance is increased. Airflow may then be reduced for operator comfort without sacrificing much performance. With pulsed DC, it is important to cycle at least two or three times per second to prevent harmful voltage swings on the object being protected.
- Steady-state DC Ionisers
Steady-state DC ionisers also employ separate power supplies and emitters, but instead of alternating positive and negative, both supplies are on all the time as the name implies. As would be expected, there is some degree of recombination, however, the ion density is still greater because of continuous operation of both supplies. The offset or balance voltage at the output will normally be more consistent than pulse units.
There are also nuclear types of ionisers which are non-electric. They are more frequently used in flammable or explosive environments for applications other than electronics.
- Room Ionisation
This type of configuration will typically have multiple emitters just below ceiling height and will rely on some amount of air movement for moving the ions down to bench level. It used to be considered as the most effective way to protect large areas against ESD hazards. However, these days localised workstation ionisation is recommended:
- Product sensitivity has become much greater and long decay times of room ionisation cannot be tolerated.
- With room ionisation often only a fraction of the ionised area may be ESD sensitive. Localised ionisers bring protection to the areas where it’s needed and performance is often 10 times faster than the ceiling height system.
- Localised ionisation moves with the workstation (or to a new workstation) making it much more flexible with changing production line layouts.
Advantages Disadvantages + Effective for large areas – Long decay times – Cannot easily be moved once set-up
- Workstation Ionisers
These come in many shapes and sizes. Probably the best known type is the bench top ioniser which is about the size of an iPad mini and about 10cm deep. They’ve been around for many years and are to this day still in high demand. Over the years, smaller and lighter units were developed. As workstation space is incredibly valuable, many users prefer the smaller units. Some bench top ionisers can even be suspended above the bench using a flexible mounting arm.
Whatever style is chosen, care should be taken to assure that items normally on the bench would not obstruct the flow of ionised air.
A Bench Top Ioniser mounted using an adjustable arm
A real benefit of bench top ionisers is the fact that they can easily be moved between workstations. So if you only have a small EPA with a few users and shared workload, you can save money by moving one ioniser between different benches.
Advantages Disadvantages + Compact – Potential obstruction of air flow + Lightweight + Portable
- Overhead Ionisers
Overhead ionisation was established to solve the problem of items on a bench blocking the flow of ionised air. Overhead ionisers have a unique hanging capability and are suspended about 45cm to 60cm above the bench – either by hanging from chains or by using mounting brackets attached to a shelf or bench.
Example of an Overhead Ioniser
Using this method of ionisation makes it very unlikely for items to block the flow of ionised air to the item being protected. In addition, the downward airflow is more consistent over the entire bench. To ensure that adequate air is delivered an overhead ioniser with 2 to 4 fans should be used. Overhead Ionisation are ideal for areas where bench space is limited.
Advantages Disadvantages + Large & consistent air flow coverage – Heavy + Don’t take up valuable workspace + Items unlikely to block air flow
- Forced Air Ionisers
Most companies address ElectroStatic Attraction, visual imperfections and contamination issues by dislodging charged dust and debris with compressed air ionisers. They use compressed air or nitrogen to neutralise static charges in localised areas – they are a quick “point-and-shoot” option. They are either hand-held or may be mounted in a fixed location.
Example of an Forced Air Ioniser
The main advantage of this type is that the user has the benefit of a strong air blast (20 to 100 P.S.I.) to help dislodge contamination, while the ionisation in the air stream eliminates the static attraction of the particles at the same time. Hand-held air nozzle types will usually have a trigger or push-button to activate the air and ion flow, while the stationary-mounted type is frequently remote controlled with a foot pedal, photo sensor or some other switch closure.
Advantages Disadvantages + “Point-and-shoot” operation – Use valuable workstation space + Strong air blast
What type of ioniser you choose depends on a lot of different factors. There is no right or wrong – just different options.
A few things you should consider before making any decisions:
- Type of operation
Depending on the work your operators are doing, one type/configuration of ioniser may have more benefits then another. For example, if your workspace is limited, an overhead ioniser might be the answer. On the other hand if there is an issue with debris & dust in your operation, then a compressed air ioniser would be better suited.
- Features required
Does your ioniser need to be made of stainless steel? Does it need to use zero-volt technology? Do activities need to be monitored and recorded with some sort of software? Make a list of what is an absolute must and where you can compromise – see next point.
- Available budget
Even though this one is the last one in this list, it by no means is the least important factor. Quite contrary, it’s generally one of the main considerations when investing in an ioniser. However, it kind of goes hand in hand with the previous 2 points. So you may have to make compromises, e.g. on the features, depending on what monies are available…
Ionisation is one of the best methods of removing charges from insulators and as a result plays an important role in controlling ESD. Remember though: an ioniser is a secondary form of defence and does not eliminate the need for standard ESD control devices such as wrist straps, heel grounders and work surface mats. It is only one element in an effective ESD programme.
Also, ionisers require periodic cleaning of emitter pins and the offset voltage must be kept in balance. Otherwise, instead of neutralising charges, if it is producing primarily positive or negative ions, the ioniser will place an electrostatic charge on items that are not grounded.