Material level indicating apparatus with status light and external test features

Apparatus for indicating level of material in a vessel that includes a probe for placement in the vessel at a position corresponding to a desired height at which material level is to be detected. Electronic circuitry is coupled to the probe, and is responsive to operating characteristics of the probe for sensing a change of such operating characteristics between a first operating characteristic at which material is spaced from the probe, and a second operating characteristic when material is adjacent to the probe. The electronic circuitry is contained within a closed housing mounted on the probe, and is connected to a source of electrical power positioned remotely of the vessel. A pair of status lamps are positioned on the housing, and are coupled to the electronic circuitry for respectively indicating application of electrical power to the circuitry and detection of one or the other of the operating characteristics at the probe. A reed switch is positioned within the housing, and is responsive to juxtaposition of a magnet externally of the housing for simulating one of the operating characteristics of the probe independently of actual material level at the probe.

The present invention is directed to devices for indicating a predetermined 
level of material in a storage container--i.e., so-called point-level 
indicating devices, as distinguished from continuous level indicating 
devices. 
BACKGROUND OF THE INVENTION 
A number of devices have heretofore been proposed and made commercially 
available for indicating point-level of material in a storage container or 
vessel. For example, U.S. Pat. No. 3,625,058 discloses a device of this 
character in which a tuning fork is positioned at a predetermined height 
within the vessel at which material level indication is desired, and is 
coupled to a motor for vibrating the fork. When material is spaced from 
the fork, the fork is free to vibrate. However, when the material reaches 
the level of the fork and covers the fork, vibration is damped. Thus, the 
fact that the level of material in the vessel has reached the height of 
the fork may be detected as a function of vibration characteristics of the 
fork itself. 
U.S. Pat. No. 3,834,235 discloses a device in which an optical probe is 
positioned at the desired height of material level detection in the 
vessel. Light energy is directed into the probe from externally of the 
vessel. When material is spaced from the probe within the vessel, the 
difference in indices of refraction between the probe material and air at 
the probe tip is such that the light energy is reflected back out of the 
vessel for detection. On the other hand, when material covers the probe 
tip, the refractive index differential at the probe tip is so altered that 
the light energy is directed into the material. Hence, the fact that 
material has reached the level of the probe tip may be detected externally 
of the vessel by absence of light energy reflected from the probe tip. 
U.S. Pat. No. 4,392,032 discloses a device of the subject character in 
which the probe takes the form of a paddle positioned within the vessel at 
the desired height of material level detection, and is connected to a 
motor carried within a suitable housing externally of the vessel. When the 
material is spaced from the paddle, the paddle is free to rotate as driven 
by the motor. However, when the material reaches the level of the paddle, 
paddle rotation is retarded, and such retardation may be detected 
externally of the vessel. 
U.S. Pat. No. 4,499,766 discloses a material level indicating device in 
which a capacitance probe is positioned within a vessel such that 
electrical characteristics at the probe vary as a function of dielectric 
properties of the material, which in turn vary as a function of material 
level. The probe is connected in an LC resonant circuit to an rf 
oscillator, and phase shift of the probe signal is monitored to indicate 
changes in material level. 
OBJECTS AND SUMMARY OF THE INVENTION 
Although devices as disclosed in the above-noted patents have enjoyed 
substantial commercial acceptance and success, improvements remain 
desirable. For example, although such devices are typically connected to a 
remote device for indicating operating characteristics and therefore 
material level within the vessel, it is desirable to provide an indication 
of operating status--e.g., application of electrical power and/or 
operating characteristics at the probe--at the device itself. This would 
assist an operator in determining status at individual vessels in a field 
of vessels without having to return to the remote status board. It is also 
desirable to provide facility for testing operation of the device from 
externally of the device without having to remove the housing cover. It is 
therefore a general object of the present invention to provide these and 
other improvements in material point-level indicating devices of the 
described character. 
Apparatus for indicating level of material in a vessel in accordance with 
the present invention includes a probe for placement in the vessel at a 
position corresponding to a desired height at which material level is to 
be detected. In the various embodiments of the invention herein disclosed, 
such probe may comprise a capacitance probe, an optical probe, a vibration 
fork, a rotating paddle or a pair of ultrasonic transducers spaced from 
each other across a material gap. Electronic circuitry is coupled to the 
probe, and is responsive to operating characteristics of the probe for 
sensing a change of such operating characteristics between a first 
operating characteristic at which material is spaced from the probe, and a 
second operating characteristic when material is adjacent to the probe. 
The electronic circuitry is contained within a closed housing mounted on 
the probe, and is connected to a source of electrical power positioned 
remotely of the vessel. A pair of status lamps are positioned on the 
housing and are coupled to the electronic circuitry for respectively 
indicating application of electrical power to the circuitry and detection 
of one or the other of the first and second operating characteristics at 
which level of material in the vessel is either spaced from or adjacent to 
the probe. The circuitry further includes a switch positioned within the 
housing, and responsive to application of energy through the wall of the 
housing from externally of the housing, for simulating the second 
operating characteristic of the probe independently of actual material 
level at the probe. In the preferred embodiment of the invention, the 
switch comprises a reed switch responsive to application of magnetic 
energy from a permanent magnet or the like external to the housing so as 
to simulate such second operating characteristic of the probe and 
illuminate the second status lamp.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 illustrates apparatus 10 in accordance with one presently preferred 
embodiment of the invention as comprising a capacitance probe 14 mounted 
on the sidewall of a vessel 12 at a position corresponding to the height 
at which it is desired to detect the level of material 16 within the 
vessel. Electronic circuitry 18 is carried within a closed housing 20 
mounted on probe 14 externally of vessel 12. The housing and probe 
construction are illustrated in greater detail in U.S. Pat. No. 4,499,766 
referenced above. Circuitry 18 includes an rf oscillator 22 that provides 
a periodic output signal to a phase shift amplifier 24. The output of 
amplifier 24 is connected to a parallel LC resonant circuit 26 that 
includes an inductor 28 and a capacitor 30 connected in parallel with the 
probe conductor 32 of probe 14. Thus, the capacitance probe forms part of 
resonant circuit 26. The output of oscillator 22 is also connected through 
a unity gain amplifier 34 to the guard shield 36 of probe 14. The wall of 
vessel 12 is connected to electrical ground. 
A phase detector 38 has first and second inputs connected to the outputs of 
oscillator 22 and amplifier 24 respectively. The output of phase detector 
38 is connected to the signal input of a comparator 40, which receives a 
reference input from a variable resistor 42. The output of comparator 40 
is connected through a delay 44 to a fail safe logic select amplifier 46 
that drives an LED 48. Circuitry 18 is powered by a power supply 50, which 
in turn receives electrical power from a remote d.c. power input source 52 
that is connected to supply 50 by a two-wire cable 54. An LED 56 is 
connected in series between remote power input 52 and power supply 50, and 
thus indicates application of electrical power to power supply 50 and the 
remainder of circuitry 18. LED's 48,56 are positioned in respective lenses 
58,60 in the wall 62 of enclosure 20 so as to indicate status of circuitry 
18 externally of enclosure 20. 
In operation, LED 56 is illuminated as long as power is applied to the 
detection circuitry. Assuming that material 16 is spaced from probe 14 as 
shown in FIG. 1, LED 48 is illuminated by logic select amplifier 46 if low 
level fail safe operation is selected or is extinguished if high level 
fail safe operation is selected (as would be typical). Fail safe logic 
selection is performed by an operator usually upon unit installation. 
Oscillator 22 continuously applies an rf signal to probe 14 as long as 
power is applied to supply 50. Capacitance at probe 14 increases as 
material level increases, so that the phase difference between the output 
of oscillator 22 and the output of amplifier 24 to resonant circuit 26 
correspondingly increases with material level. When this phase 
differential, reflected at the output of phase detector 38, reaches the 
level of reference 42, the output of comparator 40 switches accordingly. 
After delay 44, LED 48 is illuminated by amplifier 46 (assuming high level 
fail safe selection). In the event that the level of material 16 in vessel 
12 decreases, the phase differential at detector 38 correspondingly 
decreases, comparator 40 and amplifier 46 turn off, and LED 48 is 
extinguished. LED 56 thus indicates application of electrical power to 
circuitry 18, and LED 48 indicates point-level operating characteristics 
at probe 14. 
A normally open reed switch 64 is positioned within enclosure 20 at a 
preselected position adjacent to enclosure wall 62, and is electrically 
connected in series with a capacitor 66 across capacitor 30. The 
capacitance of capacitor 66 is selected to be equal to or greater than 
maximum capacitance of material 16 within vessel 12 when the material is 
adjacent to probe 14. Thus, when a magnet 68 is positioned adjacent to 
reed switch 64 externally of housing wall 62 so that the magnetic flux 
from magnet 68 closes the contacts of reed switch 64, capacitor 66 is 
connected to resonant circuit 26. Capacitor 66 thereby simulates operation 
of probe 14 when the level of material is adjacent to the probe, 
independent of actual material level at the probe, so as to test operation 
of the remaining circuitry 18. Thus, if circuitry 18 is operating 
correctly, positioning of magnet 68 externally adjacent to reed switch 64 
should cause illumination of LED 48. When magnet 68 is removed, LED 48 
should be extinguished (assuming that level of material 16 is remote from 
probe 14). Circuitry 18 is such that current drawn by the circuitry 
through two-wire connection 54 is at one of two essentially distinct 
levels, one level being a relatively low current level when material is 
spaced from probe 14, and the other being a higher current level when 
material is adjacent to the probe and LED 48 is illuminated by amplifier 
46. These two current levels, thus corresponding to the operating states 
at probe 14, which in turn correspond to low and high levels of material 
16, may be detected by a meter 69 or other suitable device connected in 
series between power source 52 and power supply 50. 
FIG. 2 illustrates application of the invention in an electro-optical 
point-level device of the type disclosed in U.S. Pat. No. 3,834,235. 
Reference numerals in FIG. 2 (and in FIGS. 3-5) identical to those 
employed in connection with FIG. 1 indicate identical elements. A 
transparent probe 70 is mounted on the sidewall of vessel 12 at a position 
corresponding to desired height of material level detection. Probe 70 
comprises an optically transparent element having a tapering end or tip 
72. Housing 20 is mounted on probe 70 externally of vessel 12, and level 
detection circuitry 74 is contained within housing 20. Circuitry 74 
includes a pulse generator 76 that receives power from remote supply 52 
through meter 69, two-wire interconnection 54 and LED 56 connected in 
series. The output of pulse generator 74 is connected to a light source, 
such as an LED 78. LED 78 is so positioned with respect to probe 70 as to 
direct a beam of light energy through the probe to probe tip 72. A 
photodetector 80 is likewise positioned with respect to probe 70 so as to 
receive light internally reflected from tip 72. The output of detector 80 
is connected through a normally closed reed switch 82 to a 
frequency-to-voltage convertor 84. The output of convertor 84, which is a 
d.c. voltage that varies as a function of frequency of input pulses, is 
fed to a Schmitt trigger 86. A single-pole double-throw switch 88 has one 
switch contact connected to the output of Schmitt trigger 86, and a second 
switch contact connected to the trigger output through an inverter 90. The 
common contact of switch 88 is connected in series through a resistor 92 
and LED 48 to the power input to pulse generator 76. 
In operation, pulse generator 76 drives LED 78 and generates pulses to 
probe 70 as long as power is applied to circuitry 74. When material 16 is 
below the level of probe 70, as shown in solid lines in FIG. 2, the 
difference in indices of refraction at probe tip 72 between probe 70 and 
the air within vessel 12 is such that the light energy from LED 78 is 
internally reflected at the probe tip, and is incident on detector 80. 
With reed switch 82 closed, the output pulses from detector 80 are fed to 
converter 84, which produces a voltage level sufficient to trigger Schmitt 
trigger 86. When material 16 rises to the position shown in phantom, the 
indices of refraction at probe tip 72 between probe 70 and material 16 are 
such that most or all of the light energy from LED 78 is transmitted into 
the material. Detector 80 no longer supplies pulses to convertor 84, and 
the output Schmitt trigger 86 changes states. LED 48 is illuminated at 
either a high or low level of material 16 in vessel 12, depending upon 
position of switch 88. For example, in the position shown in FIG. 2, LED 
48 is illuminated when convertor 84 is deprived of input pulses from 
detector 80, indicating a level of material adjacent to probe 70. 
Positioning of magnet 68 adjacent to reed switch 82 externally of housing 
wall 62 opens reed switch 82, and deprives convertor 84 of input pulses 
from detector 80 independently of level of material 16. As in the 
embodiment of FIG. 1, the current from supply 52 to circuitry 74 is 
essentially at two levels, one corresponding to a level at which convertor 
84 receives pulses from detector 80, and the other corresponding to a 
condition at which convertor 84 is deprived of such pulses. Thus, 
point-level of material 16 relative to probe 70 may be detected by a meter 
69 connected between power supply 52 and LED 56. 
FIG. 3 illustrates implementation of the invention in a vibrating 
tuning-fork device of the type disclosed in U.S. Pat. No. 3,625,058. The 
material probe in this embodiment comprises a tuning fork 100 coupled to a 
drive or transmitting crystal 102. Crystal 102 is driven by an amplifier 
104, which in turn is controlled by a pulse shaper 106. Pulse shaper 106 
receives power from remote supply 52 through two-wire cable 54. 
Power-indicating LED 56 is connected to the output of control amplifier 
104. A second crystal 108 is positioned adjacent to crystal 102, and is 
connected through a variable time delay resistor 110, and through a pair 
of jumpers 112,114, to respective inputs of a relay control comparator 
116. The output of comparator 116 is connected through LED 48 to the coil 
118 of a relay 120. Relay 120 has suitable normally open and/or normally 
closed switch contacts 122 for connection to circuitry external to housing 
20. A normally open reed switch 64 is connected across crystal 108, and is 
positioned internally adjacent to the wall 62 of housing 20 for coupling 
to external magnet 68 as desired. 
In operation, pulse shaper 106 energizes crystal 102 through amplifier 104 
as long as power is supplied by remote supply 52. When material is spaced 
from fork 100, the fork is free to vibrate, and such vibration is sensed 
by crystal 108. Jumper 112 or 114 is factory selected (and the other 
jumper is removed) depending on whether high level fail safe or low level 
fail safe operation is desired. When the material within vessel 12 rises 
to a level so as to contact tuning fork 100, vibration of the tuning fork 
is effectively damped, and vibration pulses are no longer received at 
crystal 108. Thus, depending upon whether low level or high level 
operation is desired, LED 48 and relay 118 are energized during one 
operating state of tuning fork 100 and crystal 108, and are de-energized 
at the other operating state. A level of material in contact with tuning 
fork 100 is simulated by bringing magnet 68 into external proximity to 
reed switch 64, which closes the reed switch contacts and effectively 
grounds the output of crystal 108. 
FIG. 4 illustrates implementation of the present invention in a rotating 
paddle bin level indicator of the type disclosed in U.S. Pat. No. 
4,392,032. The material probe 130 in this implementation of the invention 
comprises a paddle connected by a shaft 132 to a motor 134 positioned 
within housing 20 externally of vessel 12. Motor 134 is powered by remote 
power source 52, which supplies 120 VAC through two-wire interconnection 
54. LED 48 is coupled to an indicator logic circuit 136, which is 
connected to motor 134 and responsive to current passing therethrough to 
indicate a stall condition at paddle 130. Likewise, LED 56 is connected to 
circuit 136 so as to indicate application of electrical power to motor 
134. Relay 118 is connected to indicator logic circuit 136 through fail 
safe logic 138. Fail safe logic 138 and indicator logic 136 are disclosed 
in detail in above-noted U.S. Pat. No. 4,392,032. Power is supplied to 
logic 138 and relay 120 through normally closed reed switch 82, which is 
positioned internally adjacent to wall 62 of housing 20 so as to be 
responsive to external positioning of magnet 68 adjacent thereto. 
In operation, power is normally applied to motor 134, which rotates paddle 
130 within vessel 132. As long as material is spaced from paddle 130, the 
paddle 130 is free to rotate as powered by motor 134. When the material 
rises to the level of paddle 130, frictional engagement between the paddle 
and the material retards rotation of the paddle, stalling motor 134, and 
thereby indicating level of material as a function of the current drawn by 
the motor. Other methods of detecting retardation of paddle rotation are 
disclosed in U.S. Pat. Nos. 2,851,553, 3,412,887, 4,095,064, 4,147,906 and 
4,695,685. LED 56 is illuminated as long as power is applied. LED 48 is 
illuminated when the motor is stalled (assuming high level fail safe 
operation is selected, or extinguished if low level operation is 
selected). 
FIG. 5 illustrates implementation of the invention in an otherwise 
conventional point-level device in which material level is detected when 
material in a gap between ultrasonic transducers alters transmission of 
energy therebetween. Specifically, the probe 140 in the device of FIG. 5 
comprises a pair of crystals 142,144 carried within vessel 12 at a 
position corresponding to the height at which material level is to be 
detected. Crystals 142,144 are spaced from each other (by a suitable means 
not shown) so as to define a gap 146 therebetween. Crystal 142 is driven 
by an amplifier 148 that receives power from a power supply 150. Power 
supply 150 receives electrical power from remote source 52 by means of 
two-conductor interconnection 54. Crystal 144 is connected to the control 
input of amplifier 148, whereby the combination of crystals 142,144 form 
an oscillator that oscillates when material is positioned in gap 146, 
enhancing coupling between the crystals, and which terminates oscillation 
when material is spaced from gap 146, which is to say that gap 146 is 
filled with air. A detection and alarm circuit 152 is responsive to 
oscillation at amplifier 148 for energizing LED 48 and relay 120 (assuming 
high level fail safe selection), thereby indicating presence of material 
in gap 146. When such material is absent, relay 120 is de-energized and 
LED 48 is extinguished. Normally open reed switch 64 is connected across 
crystals 142,144, and is responsive to external adjacent positioning of 
magnet 68 effectively to short circuit the crystals, and thereby simulate 
presence of material in gap 146 independently of actual material level. 
Preferably, in all disclosed embodiments, reed switch 64 is positioned 
within the unit housing, as previously described in connection with each 
embodiment. However, it is within the scope of the invention in its 
broadest aspect to position such switch means remotely of the unit, 
external to the housing, for remote test of the devices.