GB2322975A

GB2322975A - An air ioniser

Info

Publication number: GB2322975A
Application number: GB9811080A
Authority: GB
Inventors: George Griffiths
Original assignee: Pifco Ltd
Current assignee: Pifco Ltd
Priority date: 1994-11-19
Filing date: 1995-11-10
Publication date: 1998-09-09
Anticipated expiration: 2015-11-10
Also published as: GB9811080D0; GB2322975B

Abstract

An air ioniser has a plastics case (30), a primary ion emitter (36) connected to a source of high voltage e.g. between -6 and -8KV, a secondary ion emitter (38) near the primary emitter (36) and connected to a negative voltage source of up to 3.4KV, whereby the secondary ion emitter (38) is at a different potential to the primary ion emitter (36), and a fan for driving ions out of the case. Charge build-up on the case is thereby prevented. There may be a plurality of primary ion emitters, each with an associated secondary emitter. The emitters may be metallic pins or needles or carbon fibres or filaments.

Description

'I'ITLE: Improvements in and relating t() air joflisers DEscRlPrloN This invention concerns improvements in and relating to air jonisers.

Air ionisers operate by raising one or more sharp metallic points or fine conducting fibres to a high voltage, whereby ions, normally negative ions, are emitted into the surrounding atmosphere hy corona discharge. When an air ioniser has a plastics case with emitter points close to helow the surface of the case, ion emission can be inhibited due to static charge build up on the plastics surface in the vicinity of the emitters resulting in reduced or even zero ion output as well as unstahle ion output.

Various proposals have been made for reducing the ahove-mentioned problem.

The voltage applied to the emitter(s) may be increased but that proves to be expensive. The plastics surface of the casing may be coated with an antistatic agent to leak away charge but that is at hest only a temporary solution. Another proposal is to make the casing out of antistatic plastics material but that only increases cost and is at best only a temporary solution. A fourth proposal is to extend the emitter points outwards of the plastics casing but the emitter needles or pins tend to be sharp and hence dangerous. Furthermore this proposal imposes an undesirable limitation on the design of air ionisers.

An object of this invention is to provide an air ioniser having a plastics case, wherein the ahove disadvantage is overcome or at least reduced in effect.

According to the invention there is provided an air ioniser having a plastics case, a primary ion emitter connected to a source of high voltage and located within the case, a secondary ion emitter having a negative voltage applied thereto of up to 3.4KV near the primary ion emitter and located within the case, whereby the secondary ion emitter is at a different potential to the primary ion emitter and a fan for driving ions out of the case.

Air ionisers of the invention may have more than one primary ion emitter and each primary emitter may he associated with its own secondary emitter.

The primary' ion emitters for use in air ionisers of the invention may he in the form of metallic pins or needles, carbon tibres or filaments or any other suitable conductive means for providing corona discharge when a high v oltage is applied thereto.

The secondary ion emitters for use in air ionisers of the inventions may he selected from the same types of material as the primary emitters.

A primary ion emitter is preferably closely spaced from a secondary ion emitter. 'typically primary to secondary' ion emitter spacings in the region of 10 to 40mm may be suitable.

The primary ion emitter is preferably connected to a source of high negative voltage so as to output desirable negative ions. Typically voltages in the range of 6.0KV to -8.OKV are applied to the primary ion emitter. Its associated secondary ion emitter may have a negative voltage applied thereto but preferahly chosen so as to optimise negative ion emission. A secondary ion emitter having a negative voltage applied thereto of upto 3.4KV has been found not to inhibit negative ion emission and at some emitter spacings and voltages in that range actually to increase negative ion emission relative to a primary ion emitter alone.

This invention will now be further described, hy way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a prior art air ioniser; Figure 2 shows the prior art ioniser with build up of static charge; Figure 3 shows an air ioniser according to the invention; and Figure 4 is a graph of net ion emission current against secondary emitter voltage for air ionisers according to the invention.

Referring to Figures 1 and 2 of the accompanying drawings. an air ioniser 10 has a plastics case 12 and one or more ion emitters 14 in the form of metallic needles or pins, carbon fibres or other conductive means for providing a corona discharge.

The ion emitters may be proud of surface 16 of the case 12, flush therewith or withdrawn relative thereto. The ion emitters are connected to a high negative voltage source in use so as to generate negative ions from the emitters.

As negative ions are produced, negative static charge builds up on the surface 16 in the vicinity of each emitter 14 as negative ions impinge on the surface 16. This negative charge build up inhibits corona discharge so that negative ion emission becomes unstable and is reduced possibly to zero.

This problem may he overcome according to the invention as exemplified in Figure 3 of the accompanying drawings by providing an air ioniser comprising a plastics case 30 having a fan 32 at one side, a grill 34 at the opposite side thereto, a primary emitter 36 connected to a source of high voltage and a secondary emitter 38 connected to a high voltage source such that the secondary emitter is positive with respect to the primary emitter. The voltage applied to a secondary emitter will be chosen so as to optimise, maximise or stahilise the total ion output into the air. The optimum voltage on the secondary emitter may depend on its distance from its associated primary emitter. Thus, the greater the distance between the primary and secondary emitters, the more positive the secondary emitter may need to be relative to its associated primary emitter.

Uhe invention will he further described hy means of the following Example Example A flat ABS plastics sheet 200 x 135mm was used to represent the plastics surface 16 of the ioniser of Figure 3 of the drawings. A pair of sharp pins were used as primary and secondary emitters, each being centrally placed in a 4mm diameter hole of depth 4mm, with their points flush with the surface of the plastics sheet. The plastics sheet was cleaned to remove surface conductivity caused by dirt or antistatic agents and mounted on a non-conducting stand away from any earthed surfaces.

A series of four experiments were carried out with primary to secondary emitter spacings of 10, 20, 30 and 40mm. In each experiment the primary emitter was at a negative potential of 7.2KV and the secondary emitter potential was varied from a negative potential of 6.7KV to earth potential. The net ion emission current was measured at different potentials for the secondary emitter for each emitter spacing and the results plotted on the graph shown in Figure 4 of the accompanying drawings.

rhe net ion emission represents the sum total of the currents from the primary and secondary emitters. In this experiment it was a measure of the free negative ions escaping into the atmosphere.

The graph shows a distinct peak of net ion emission current for each spacing 10, 20, 30 and 40mm which is surprisingly substantially higher than the "float" current which effectively represents ion emission current without a secondary emitter.

Thus, it may be possible by means of the present invention to achieve higher ion output than from a primary emitter alone and that output may be optimised by selection of primary and secondary emitter spacings and/or hy selection of secondary emitter applied voltage relative to primary emitter applied voltage.

It should be appreciated herein that references to applied voltage for the secondary emitters may include connection thereof to earth potential i.e. where the applied voltage is zero.

Attention is directed to our copending patent application GB2295278A, from which this application has heen divided.

Claims

( LAIMS

I. An air ioniser having a plastics case a primary ion emitter connected to a source of high voltage and located within the case, a secondary ion emitter having a negative voltage applied thereto of up to 3.4KV near the primary ion emitter and located within the case, whereby the secondary ion emitter is at a different potential to the primary ion emitter and a fan for driving ions out of the case.
2. An air ioniser as claimed in claim 1 having a plurality of primary ion emitters.
3. An air ioniser as claimed in claim 2. wherein each primary ion emitter is associated with its own secondary ion emitter.
4. An air ioniser as claimed in claim 1. 2 or 3, wherein the or each primary emitter is in the form of a metallic pin or needle or of a carbon fibre or tilament.
5. An air ioniser as claimed in any one of claims I to 4, wherein the or each secondary emitter is in the form of a metallic pin or needle or of a carbon tibre or filament.
6. An air ioniser as claimed in any one of claims 1 to 5, wherein the primary emitter and its associated secondary emitter are spaced apart by 10 to 40 mm.
7. An air ioniser as claimed in any one of claims 1 to 6, wherein the primary emitter is connected to a source of high negative voltage.
8. An air ioniser as claimed in claim 7, wherein voltages in the range of -6.0KV to -8.0KV are applied to the primary emitter.
9. An air ioniser substantially as hereinhefore described with reference to and as illustrated in Figure 3 of the accompanying drawings.