Roll filter metering arrangement

A metering arrangement for limiting the advance of the filter media in an automatic roll filter having a timer which periodically energizes a drive motor adapted to draw the media through the filtering zone of the apparatus. The arrangement includes a metering reel which is adapted to rotate in direct proportion to the lineal advance of the filter media, a magnet mounted on the reel which generates a magnetic field limited to a predetermined arc of the periphery of the reel, and a reed switch which is actuated by the magnetic field to signal an electrical circuit to shut off the drive motor after a preselected increment of the filter media has been drawn into the filtering zone of the apparatus.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to automatic roll filters and in particular 
to an improved metering apparatus for regulating the advance of the filter 
media in such devices. 
2. Description of the Prior Art 
The prior art discloses a variety of metering arrangements for regulating 
the advance of roll filter media through the filtering zone of an 
automatic roll filter. For example, U.S. Pat. No. 3,276,191 shows the use 
of a weighted drive chain adapted to advance clean filter media into the 
filtering zone upon displacement of a roller mechanically connected with 
the chain. In that arrangement, the media is drawn over the roller in a 
fashion, such when the dust loading in the media reaches a predetermined 
level, the gas pressure on the media causes the media to displace the 
roller which in turn releases the chain to advance the media. U.S. Pat. 
No. 3,310,921 shows another metering arrangement wherein a drive motor is 
connected to suitable timing and dust load sensing circuitry which 
includes an electrical shut-off switch actuated by a cam adapted to rotate 
with the movement of the filter media across the filtering zone. Each time 
the circuitry activates the drive motor, the cam allows the media to 
advance a predetermined distance into the filtering zone and then actuates 
the switch to shut off the motor. While mechanical metering arrangements 
such as the foregoing have proven satisfactory in many applications, 
experience has shown that they have been susceptible to misadjustment in 
the field as well as being subjected to the deleterious effects of wear 
and corrosion of their various components. 
SUMMARY OF THE INVENTION 
The present invention relates to a metering arrangement for a filter media 
advance control system in an automatic roll filter apparatus. 
The automatic roll filter apparatus in which the switching arrangement is 
to be used includes a filter housing wherein filter media is drawn off a 
roll of media on one side of an air filtering zone and rewound on a rewind 
spool on the other side of the filtering zone. During normal filtering 
operations, a motor connected to the rewind spool is periodically 
energized by an electrical circuit connected to the motor to advance new 
filtering media into the filtering zone. 
The metering arrangement embodying the invention is connected with the 
electrical circuit and is adapted to signal the circuit to turn off the 
motor to limit the advance of the filter media to preselected increments. 
The arrangement includes a metering reel mounted within the housing which 
is adapted to rotate in direct proportion to the lineal advance of the 
filter media, a magnet mounted on the reel which generates a magnetic 
field which is limited to a predetermined arc of the periphery of the 
reel, and a proximity sensor such as a reed switch connected with the 
electrical circuit mounted in the housing proximate the magnet. This 
allows measuring the advance of the filter media by monitoring the 
position of the magnet with the proximity sensor which in turn signals the 
circuit to shut off the motor when the desired incremental advance has 
been made. 
Considering the foregoing, it can be seen that the invention contemplates a 
metering arrangement which is easy to adjust and maintain in the field as 
well as being relatively immune to the wear and corrosion problems 
encountered with the mechanical devices heretofore in use. However, it is 
to be understood that various changes can be made in the arrangement, form 
and construction of the apparatus disclosed herein without departing from 
the spirit and scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings, the filter media advance control system 1 
embodying the metering arrangement 2 of the invention is utilized in an 
automatic roll filter apparatus 3. The filter apparatus 3 includes a 
housing 4 having a filter media supply zone 5, a central filtering zone 6, 
and a filter media rewind zone 7. A roll 8 of tightly wound filter media 
is mounted in the supply zone 5. The filter media can be any one of a 
variety of commercially available filtering materials. For example, media 
formed of an expansible-compressible fiberglass such as that used in the 
air control unit shown in U.S. Pat. No. 3,310,931 discussed above in 
regard to the prior art would be suitable for this purpose. 
As is well known in the art, during filtering operations, a web of filter 
media 9 from the roll 8 is advanced incrementally from time to time into 
and through the central filtering zone 6 where the gas stream flows 
through the media. As the web of filter media 9 is progressively advanced 
through the central air filtering zone 6, the web assumes an expanded 
thickness of comparatively three-dimensional proportion to filter the 
contaminates from the gas stream. The web 9 is then correspondingly 
progressively advanced to the rewind zone 7 where it is tightly wound upon 
a rewind spool 10 driven by a suitable electric motor 11 operatively 
connected to the rewind spool 10 by a chain and sprocket arrangement or 
other conventional means. As will be described, the motor 11 is energized 
by the electrical circuit 12 shown in FIG. 5 to periodically advance the 
filter media during filtering operations. 
Referring to FIGS. 3 and 4, the metering arrangement 2 includes a metering 
reel 13 rotatably mounted in the supply zone 5 in a suitable form of 
journal box (not shown). The web of filter media 9 is arranged to pass 
over the metering reel 13 before the media enters into the central air 
filtering zone 6. This causes the reel 13 to rotate in direct proportion 
to the lineal advance of the media into the central air filtering zone 6. 
As shown in FIG. 3, the metering reel 13 is of a circular, spider-like, 
cross-sectional configuration formed by a plurality of outwardly radiating 
ribs 14 which carry the media as it passes over the reel. This arrangement 
accommodates securing a pair of magnets 15 adapted to selectively trigger 
the electrical circuit 12 to control the advance of the filter media into 
the air filtering zone 6. As can be seen from the drawings, the magnets 15 
are secured to one end of the metering reel 13 in radial alignment on 
opposite sides of the reel. Each of the magnets 15 is affixed by a pair of 
ties or straps 16 to a generally U-shaped bracket 17 nestled between a 
pair of adjacent ribs 14 inward of the outer periphery of the reel and 
releasably secured to the ribs by a pair of spring-loaded clips 18 which 
clamp the sides of the bracket to the ribs. 
Although the metering arrangement 2 can be used with a variety of 
electrical circuits to control the motor 11, a schematic of one circuit 
suitable for controlling the motor is shown in FIG. 5. As shown in the 
drawing, the secondary coil of a transformer 20 is connected to a DC 
rectifier 21 having one side connected to a normally closed on/off switch 
22 and a normally closed media runout switch 23 connected in parallel with 
the switch 22, both of which are in turn connected to the inputs of an AND 
gate 24. The runout switch 23 is kept closed during normal filtering 
operations; however, when all the filter media is drawn off the roll 8 it 
opens to interrupt the circuit through the switch to the AND gate 24. U.S. 
Pat. No. 3,350,853 discloses a mechanical runout switch mounted in the 
supply zone of the filter arrangement shown in that patent which 
experience has shown to be suitable for this purpose. 
The output of the AND gate 24 is connected to a normally open reed switch 
25 and a repeating cycle digital timer 26 connected in parallel with the 
reed switch 25. As best shown in FIG. 3, the reed switch 25 is supported 
by a bracket 27 mounted on the side of the housing 4. The reed switch 25 
is aligned with the magnet 15 and is spaced from the axis of the metering 
reel 13 at a distance where it will be closed by the magnetic fields 
generated by the magnets 15 within about a 45 degree arc on either side of 
the magnets about the periphery of the reel, and open when the reel is 
rotated so that the reed switch is outside those fields. The reed switch 
25 and the timer 26 are in turn connected to the inputs of an EXCLUSIVE/OR 
gate 28 which has its output connected to one side of the operating coil 
of a control relay 29 which has its other side connected to the other side 
of the rectifier 21. As will be described, when the control relay 29 is 
energized, it completes the circuit from the primary side of the 
transformer 20 to the motor 11 which begins turning the rewind spool 10 to 
advance the filter media until the metering arrangement 2 signals the 
circuit to de-energize the relay. 
In the typical roll filter installation, the filter media is advanced about 
21/2 inches a day. This of course will vary from one installation to the 
next depending on the quality and quantity of air being cleaned. However, 
the operating cycle of the advance control system will remain essentially 
the same. 
Assuming the output from the timer 26 is initially "0" with the reed switch 
25 open, the Q.sub.1 and Q.sub.2 inputs into the EXCLUSIVE/OR gate 28 are 
both "0" so that its output is "0". In this condition, the control relay 
29 is de-energized and the motor 11 is off. When the digital timer 26 
completes the first half of its timing cycle, its output is switched to 
"1". With Q.sub.1 and Q.sub.2 at the EXCLUSIVE/OR gate 28 now "0" and "1", 
respectively, its output is "1". This results in energization of the 
control relay 29 which turns on the motor 11 which begins turning the 
rewind spool 10 to advance the filter media. As the media advances, it 
turns the metering reel 13 until one of the magnets 15 is moved close 
enough to the reed switch 25 for its magnetic field to close the switch. 
When this occurs, Q.sub.1 at the EXCLUSIVE/OR gate 28 changes to "1" 
resulting in the gate's output changing to "0" with the consequent 
de-energization of the control relay 29 which stops the motor 11. This 
condition is maintained for the second half of timing cycle. Then, when 
the timer 26 completes its cycle, its output changes to "0" so Q.sub.1 and 
Q.sub.2 at the EXCLUSIVE/OR gate 28 are "1" and "0", respectively. In this 
condition, the output from the EXCLUSIVE/OR gate 28 is "1" which results 
in energization of the control relay 29 which turns on the motor 11 to 
advance the media again. The motor 11 continues to run until the magnets 
15 are carried to a position where their magnetic fields no longer affect 
the reed switch 25 which allows it to open. When this occurs, Q.sub.1 
changes to "0". Thus, both Q.sub.1 and Q.sub.2 are "0" so that the output 
from the EXCLUSIVE/OR gate 28 is again "0" and the control relay 29 is 
de-energized. This turns off the motor 11 to stop the advance of the 
filter media and thus completes one cycle of the digital timer. 
During normal filtering operations, both the on/off switch 22 and the 
runout switch 23 are closed. As long as both of these switches are closed, 
the timer 26 continues to repeat the foregoing cycle to periodically 
advance the filter media. However, as can be appreciated, if either or 
both of these switches are opened, the output from the AND gate 24 changes 
to "0" and the circuit is de-energized.