ion generator circuits

Book Abstract by: P03

Original Author: P03

Summary rating: 2 stars (1 Ratings)
Visits : 148
words:900
Comments : 0

Build An Ion Detector
by Vincent Vollono from "Spring 1994 Electronics Hobbyists Handbook"
Ions
are defined

as electrically charged atoms. Positively charged ions have
a deficiency of electrons, and negatively charged ions have a surplus
of electrons. An ion can also be classified as an atom or molecule with
an electrostatic charge. Another classification of an ion is a charged
particle that is formed when one or more electrons are taken from or
added to a previously neutral atom or molecule.
The Ion Detector described in this article can be used to
detect the presence, and indicate the relative amount, of free ions in
the air. The Ion Detector, a handheld unit about the size of a pack of
cigarettes, is designed to indicate ion emissions from ion generators
high-voltage leakage points, static-electricity sources, electric-field
gradients, and in other situations where the presence of their relative
flux density is required.
The front cover features, a sensitivity control with on-off
switch, a high flux indicator lamp, and a panel meter. An antenna,
mounted on the top of the unit, serves an external ion collector. A
strip of metallic foil on the outside of the plastic enclosure touches
the users hand and is used to ground the unit. For fixed applications,
the strip can be replaced by a wire connected to the ground.
Circuit Description. Figure 1 shows a schematic
diagram of the Ion Detector - a rather simple circuit consisting of
three transistors (two PN2907 PNP units, and a single PN2222 NPN unit),
three resistors, an antenna, and an LED.
In that circuit, a telescoping antenna is used as the pickup.
In the presence of an ion field, ions accumulate on the antenna,
causing a minute negative current to flow to the base of Q1. Capacitor
C1 and resistor R1 form an RC network, whose function is to eliminate
any rapid fluctuations. Once the negative current becomes large enough,
it causes Q1 to turn on, connecting the negative terminal of battery B1
to the base of Q2. That forward biases Q2, causing it to turn on. That,
in turn, couples the base of Q3 to the positive terminal of the
battery, forward biases Q3 - whose collector is in series with
current-limiting resistor R2 and meter-sensitivity control R3 - causing
it to conduct.
With Q3 turned on, meter M1 indicates (in a non-linear manner)
the relative level of ion flux, while LED1 (which is connected in
series with Q3''s emitter) lights to give a visual indication of strong
ion fields. It should be noted that in order for the unit to operate
properly, some sort of ground is usually required.
Metallic tape is used in the prototype to provide a convenient
contact for the users hand, thereby providing a partial ground. If
possible, such as when the unit is used as a monitor at a permanent
location, the detector should be grounded to a water pipe, or some
other convenient grounding point.
The detector is set up to detect negative ions. It can be made
to detect positive ions by simply reversing the polarity of the
transistors that comprise the circuit, i.e., PNP units become NPN
units, and NPN transistor is replaced by a PNP unit. It should not that
the performance of the detector is seriously affected by high humidity.
Damp or moist air tends to impair the circuits ability to detect ion
flux.
The Ion Detector can be used to give a quick indication of the
presence of a negative ion field, aid in identifying its source, and
indicate its relative strength, but it is not designed to provide an
absolute measurement of flux intensity. The circuit can also be used to
aid in making adjustments to ion sources, by noting the meter''s needle
Ion Detector can also be used to ferret out residual ion fields, check
for ion leakage (in shielding tests, for example), or to test for
static charges (in people''s clothes, fluorescent lighting, plastic
containers, certain winds, etc.), along with a host of other
applications.
Fig. 1. The Ion Detector is a rather simple circuit consisting
of three transistors, (two Pn2907 PNP units, and a single PN2222 NPN
unit), three transistors, a telescoping antenna (which is used as a
pickup), and a LED.
Parts List For The Ion Detector
Q1, Q2
PN2907 general-purpose PNP silicone transistor
Q3
PN2222 general-purpose NPN silicone transistor
LED1
Light-emitting diode
R1
100-megohm, 1/2-watt, 5% resistor
R2
10,000-ohm, 1/4watt, 5% resistor
R3
5000-ohm potentiometer (see text)
C1
470-pF, ceramic-disc capacitor
M1
100-mA panel meter
B1
9-volt transistor-radio battery
S1
see text
ADDITIONAL PARTS AND MARTERIALS
Perfboard materials, plastic enclosure, 9-volt battery holder and connector, wire, solder, hardware, etc.
Construction.
The author''s prototype of the Ion Detector was assembled on a section
of perfboard, using point-to-point wiring for inter component
connections. Pay close attention to the orientation of the polarized
components (diodes, transistors, electrolytic capacitors, etc.), as
well as the polarization of the DC source that will power the circuit
when assembling the circuit. It is very important that you verify all
your interconnecting wiring.
It is highly recommended that the circuit be enclosed in a
plastic project box. Once the circuit is completed, a 1/2 inch wide
strip of aluminum is attached to the side of the enclosure, and is then
connected to the circuit board (at the junction of C1, the positive
lead of the panel meter, and the positive terminal of the battery) as
shown in Fig. 1. The aluminum strip serves as the circuit''s grounding
point. The grounding strip can be replaced or supplemented by a wired
alligator clip for connection to a "true" earth ground ( a water pipe,
for instance).
The author used a telescoping antenna as the ion pickup in his
prototype unit; however, a piece of stiff wire (a wire hanger, for
example) would also work. In either case, the antenna must be
electronically isolated; i.e., it should not be connected to ground in
any way. Note that S1 (the on-off switch) is piggy-backed to
potentiometer R3 (a 5K potentiometer that serves as the meter''s
sensitivity control). You can also use a potentiometer with a
piggy-back switch or use two separate components.
For meter M1, the author used a small 100-mA panel meter; using
a meter with a rating other than that specified may affect the
performance of the unit. It is also important to remember that any
leakage around the input of Q1 will reduce the circuit''s sensitivity.
To help prevent (or at least reduce) leakage, the circuit can be coated
with a high-quality varnish. If you decide to coat the circuit, make
sure that the unit is completely clean and dry before applying the
varnish.
Use. To demonstrate the unit''s sensitivity, run a
plastic comb through your hair, and place it near the antenna of the
Ion Detector. Making sure that the unit is grounded (either by the user
touching the aluminum strip or by connecting an earth ground to the
circuit), bring the comb near the antenna. As t