U.S. patent number 3,858,102 [Application Number 05/431,209] was granted by the patent office on 1974-12-31 for light load control for well pump.
Invention is credited to James L. Quinn.
United States Patent |
3,858,102 |
Quinn |
December 31, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
LIGHT LOAD CONTROL FOR WELL PUMP
Abstract
A control for turning on and off a motor driving a well pump
which includes high pressure and low pressure detectors. The
detectors are coupled to the gate circuits of respective silicon
controlled detectors, or SCR's, which have their load circuits
connected in a latching loop circuit which energizes a relay to
operate the motor. To disable the relay when the pump is sucking
air, an auxiliary SCR controls an auxiliary relay having normally
closed contacts connected in the loop circuit. The auxiliary SCR is
turned on by a source of positive voltage but a current transformer
wired in series with the pump motor sets up a negative control
voltage which is of sufficient level under normal current
conditions to overpower the positive voltage to maintain the
auxiliary SCR turned off. A capacitor connected to the gate insures
against premature actuation of the gate by positive inrush
voltage.
Inventors: |
Quinn; James L. (Chicago,
IL) |
Family
ID: |
27000335 |
Appl.
No.: |
05/431,209 |
Filed: |
January 7, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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359102 |
May 10, 1973 |
3801889 |
Apr 2, 1974 |
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Current U.S.
Class: |
318/474;
307/118 |
Current CPC
Class: |
G05D
16/2066 (20130101) |
Current International
Class: |
G05D
16/20 (20060101); G05b 013/00 () |
Field of
Search: |
;318/481,482,474
;307/118 ;417/36,38 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schaefer; Robert K.
Assistant Examiner: Ginsburg; M.
Attorney, Agent or Firm: Wolfe, Hubbard, Leydig, Voit &
Osann, Ltd.
Parent Case Text
This is a division of application Ser. No. 359,102, filed May 10,
1973, now U.S. Pat. No. 3,801,889, issued Apr. 2, 1974.
Claims
I claim as my invention:
1. In a control for the circuit for a motor driving a well pump
having an associated tank and intended for operation from the
regular a.-c. supply line, a low-current lockout comprising, a
current transformer having its primary winding wired in series with
the pump motor and having a secondary winding, an latching type
relay having an input coil and having a normally closed output
contact, connecting means between the output contact and the motor
so that the output contact controls the flow of current to the
motor, a current detector circuit having an SCR including a gate
and load circuit, the load circuit being coupled to the input of
the latching type relay, the current detector circuit having power
input terminals connected in shunt with the motor, the current
detector circuit further having a source of positive voltage
supplied by the power input terminals and capable of turning the
SCR on and having a source of negative voltage supplied by the
secondary winding of the current transformer, means for coupling
the gate of the SCR to both sources, the source of negative voltage
varying in accordance with the motor current and of such magnitude
as to keep the SCR turned off as long as rated current is drawn by
the motor but which permits the SCR to be turned on when less than
rated current is drawn by the motor with resultant actuation of the
latching type relay and interruption of the motor circuit for
disablement of the motor under conditions when the pump is sucking
air.
2. The combination as claimed in claim 1 in which means are
provided for preventing inrush of positive voltage to the SCR when
the motor is turned on so as to permit development of negative
voltage corresponding to rated motor current to maintain the SCR
turned off.
3. The combination as claimed in claim 1 in which a capacitor is
connected from the gate to the cathode of the SCR so as to prevent
the gate from going positive and hence turning on the SCR prior to
the time that negative voltage is applied at the gate by reason of
voltage induced in the secondary winding of the current
transformer.
Description
It is an object of the present invention to provide a control for a
well pump which is reliable in turning the pump motor on at a
predetermined low pressure and off at a predetermined high pressure
and which positively disables the motor when the pump begins to
suck air. It is another object to provide a control system for a
well pump which makes use of the solid state SCR devices but in
which such devices are completely deenergized during the long
periods of standby when the pressure in the tank is up to the rated
level. It is a general object to provide a control circuit for a
well pump which is capable of operating without care of maintenance
for long periods of time.
Other objects and advantages of the invention will become apparent
upon reading the attached detailed description and upon reference
to the drawings in which:
FIG. 1 is a diagram showing a typical well pump system to which the
invention is applied.
FIG. 2 is a schematic diagram illustrating a preferred embodiment
of the invention.
While the invention has been described in connection with a
preferred embodiment, it will be understood that I do not intend to
be limited thereto but intend on the contrary to cover the various
alternative and equivalent forms of the invention included within
the spirit and scope of the appended claims.
Turning now to the drawings, a control package indicated at 10
serves to control a motor M driving a pump P which furnishes water
under pressure to a tank T. Communicating with the tank are
detectors H and L which are set to respond at respective high and
low pressures, or water levels, and which are connected to
terminals 11, 12, sharing a common terminal 13. The motor is
powered through terminals 14, 15 and power is received from lines
L1, L2 via terminals 16, 17. The water W, kept under head of air,
leaves the tank through an outlet 18. It will be understood that
detectors H and L include switches which show an open circuit when
"satisfied," a drop in pressure closing the circuit to "call for
water."
Turning now to FIG. 2, a first SCR 20 is provided having an anode
21, a cathode connection 22 and gate 23. The gate is connected to
the low pressure detector L via a series resistor 24. The resistor
25 is the usual gate-cathode resistor and the diode 26 serves as a
clamp to limit the negative voltage which can be applied to the
gate.
Under the control of the high pressure detector H is an SCR device
30 having anode 31, cathode connection 32 and gate 33, the latter
being connected to the high pressure detector via a series resistor
34 and with the gate being provided with a shunting resistor 35 and
a clamping diode 36.
For the purpose of furnishing load current, a transformer 40 is
provided having a primary winding 41 and a secondary winding 42.
Connected in series, that is, in a loop, with the load circuits of
the SCR's and with the transformer secondary winding is a motor
relay having an input circuit, or winding, 50 and normally open
contacts 51, 52 which are connected in series with the a.-c. supply
lines. A protective diode 53 connected across the relay protects
the SCR's against the inductive kick which occurs when the relay is
deenergized.
In order to make the SCR 20 operate in the latching mode, such SCR,
and the relay winding 50 which is in series with it, are shunted by
a capacitor 54. Thus during positive pulses of current, the
capacitor is charged to a voltage which corresponds to the sum of
the voltage drops through the relay winding and anode-cathode
circuit. The capacitor has a sufficiently high capacitance so as to
maintain a positive voltage between the anode 21 and cathode 22,
thereby to maintain the SCR 20 in the conductive state, bridging
the negative half cycles supplied from the upper end of the
transformer winding 42.
For the purpose of protecting the pump against the hazardous
condition of "sucking air," means are provided for disabling the
pump motor when the motor is turned on but when substantially less
than rated current is flowing through the motor. This is
accomplished by a current detecting circuit which employs an
auxiliary SCR 60 having an anode 61, cathode 62 and a gate 63, the
latter having a shunt resistor 64. The auxiliary SCR 60 is
connected to operate an auxiliary relay having input and output
circuits in the form of coil 65 and a normally closed contact 66.
The relay is of the mechanically latching type having a latch 67
which serves to "hold in" the relay armature following energization
with a reset button 68 provided for manual release. Connected in
parallel with the relay coil is a protective diode 69.
For controlling the auxiliary SCR 60, that is, for keeping the same
non-conductive as long as normal current is drawn by the motor M, a
current transformer 70 is provided having a primary winding 71
which is wired in series with the motor and a secondary winding 72.
Voltage from the secondary winding is rectified by a diode 73 and
the level of the rectified voltage is set by a potentiometer 74
having a wiper 75, which wiper is connected via a series resistor
76 to the gate 63 of the auxiliary SCR. The diode 73 is so
polarized that rated current, drawn by the motor, is effective to
produce a negative voltage at the gate 63 of the auxiliary SCR
which is sufficiently high as to keep the SCR turned off. However,
for turning on the SCR when lower values of motor current are
drawn, indicating the condition of sucking air, a positive source
of voltage is provided which is made up of a diode 80 and series
resistor 81. The diode 80, and the auxiliary SCR are powered
through input terminals 82, 83 which are connected to the
"switched" side of the contacts 51, 52 so that the current
detecting circuit is completely dead and unresponsive during the
times that the motor M is turned off.
In order to prevent the auxiliary SCR 60 from responding to an
inrush of positive voltage when the contacts 51, 52 are initially
closed, and before negative control voltage is developed by the
current transformer and its associated diode, a high value
capacitor, indicated at 90, is connected to the gate terminal of
the SCR and specifically between the gate and cathode terminals.
The capacitor increases the effective time constant of the gate
circuit since no positive voltage can be developed at the lower end
of the resistor 81 until the capacitor 90 has had opportunity to
charge, and the rate of positive charging is limited by the value
of the resistor 81. Once the initial inrush condition has been
taken care of, the voltage across the capacitor will stabilize at a
voltage and polarity which depends upon the relative magnitude of
the voltages being supplied via the "negative" diode 73 and
"positive" diode 80, the negative voltage normally
predominating.
While the operation of the circuit will be apparent from the
foregoing description, it will be helpful to review a typical
operating sequence. Let it be assumed that the system occupies the
initial condition shown in FIG. 1 with water at a low level within
the tank and with a low pressure in the space above it, causing
both of the detectors to be turned on, or closed, "calling for
water." It is apparent that closure of the contacts L and H (FIG.
2) provides a path for positive control voltages to pass to the
gates 23, 33 at the same time that positive pulses are applied to
the anodes so that both SCR's conduct, and serve with one another,
to energize the winding 50 of the motor relay, closing contacts 51,
52 and turning the motor on. The resultant operation of the pump
then causes water to flow into the base of the tank to raise the
water level and the pressure of the contained air.
When the pressure of the air becomes sufficient to satisfy the
detector L, the latter becomes open circuited, thus deenergizing
the gate terminal 23 of the SCR 20. However, because of the
latching effect of the capacitor 54 the SCR 20 will continue to
remain conductive and pressure will further increase until the high
pressure detector H is finally satisfied opening its circuit (FIG.
2) and deenergizing the gate 33 of the SCR 30. Since the latter
operates in the non-latching mode, such SCR will become
non-conductive and no further current will flow through the loop
circuit formed by the SCR's, causing the motor relay 50 to drop
out, opening contacts 51, 52 and denergizing the motor. This causes
the control circuitry to go into the quiescent state.
However, as water is drawn through the connection 18 from the tank
the pressure will be gradually reduced until the detector H will,
calling for water, close its circuit. No current will, however,
flow through the loop circuit since the SCR 20 remains deenergized.
However, when the water pressure falls an additional "differential"
amount, the low pressure detector L, too, calls for water by
closing its circuit thereby energizing the gate 23 so that the
condition for conduction is satisfied in both of the SCR's thereby
energizing the motor relay 50, closing contacts 51, 52 and turning
on the motor.
The initial positive inrush through the diode 80 to the gate 63 of
the auxiliary SCR is defeated by the capacitor 90. At rated motor
current, the voltage generated in the current transformer and
rectified by the diode 73 insures that a net negative voltage will
exist at the gate 63 thereby maintaining the auxiliary SCR 60
turned off, and the auxiliary relay deenergized so that the loop
circuit, including contact 66, remains intact.
However, let it be assumed that water cannot be replenished at a
sufficient rate within the well to keep up with the rate of
withdrawal by the pump, in which case the pump will "suck air."
Such sucking of air effectively unloads the pump, and hence the
motor, so that the current through the motor falls to only a
fraction of rated value. This condition is reflected by a drop in
voltage at the output of the current transformer and hence a drop
in the negative voltage produced by the diode 73, so that the
positive voltage from the diode 80 prevails, causing the auxiliary
SCR to become conductive. This opens the contact 66 in the loop
circuit, dropping out the motor relay 50 and opening the contacts
51, 52 to turn off the motor. In carrying out the invention the
auxiliary, undercurrent relay is of the latching type so that the
contact 66 remains open circuited, thus disabling the motor until
the reset push button 68 is depressed, whereupon normal operation
and control of water pressure will resume.
It has been found that in a normal installation, in which the leads
of the detectors run closely parallel to one another, it is
possible for the closing transient which occurs when the high
pressure detector calls for water to induce a signal in the low
pressure control line 11 which is sufficient to jar the SCR 20
prematurely into conduction. In order to avoid this possibility the
time constant of the gate circuit of the transistor 20 is increased
by addition of an auxiliary capacitor 95.
The term "detector" used herein is used in a generic sense to
include both pressure-responsive devices which provide an indirect
measure of water level or means to detect level directly. Also
while the invention has been described as applied to a well pump it
will be apparent that it is applicable to any pump which serves to
replenish a reservoir.
* * * * *