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PDF ( 数据手册 , 数据表 ) QT114

零件编号 QT114
描述 CHARGE-TRANSFER QLEVEL SENSOR IC
制造商 QUANTUM
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QT114 数据手册, 描述, 功能
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QProx™ QT114
CHARGE-TRANSFER QLEVELSENSOR IC
! Limit sensing of almost any fluid or powder
! 2-Tier level sensor - Hi / Low limits with one probe
! Only one external part required - a 5¢ capacitor
! Uses internal probes or external electrodes
! Active high or active low outputs
! Slosh filter averages response of moving fluids
! LED drive capable on both outputs
! 2.5 to 5V 20µA single supply operation
! HeartBeat™ health indicator on both outputs
Vcc
Out1
Out2
Filt
1
2
3
4
8 Gnd
7 Sns2
6 Sns1
5 Pol
APPLICATIONS -
! Process controls
! Vending machines
! Automotive fluids
! Consumer appliances
! Medical fluid sensing
! Soil moisture sensing
DESCRIPTION -
The QT114 QuickLevel™ charge-transfer (“QT”) sensor IC is specifically designed to detect point level in fluids
and powders. It will project a sense field through almost any dielectric, like glass, plastic, or ceramic, to sense
level on the inside of a vessel, from its exterior. It has the unique capability of independently sensing two trip
points when used with structured electrodes having two tiers.
The QT114 does not have sensing timeouts, drift compensation, or other functions which would interfere with
level sensing. Its threshold levels are fixed, and the amount of signal required to exceed a threshold is dependent
on circuit gain and electrode size and loading, all of which are under the control of the designer.
The QT114 requires only a single inexpensive capacitor in order to function. One or two LEDs can also be added
to provide a visual sensing indication.
Power consumption is under 20mA in most applications, allowing operation from Lithium cells for many years. In
most cases the power supply needs only minimal regulation.
The QT114 employs numerous signal acquisition and processing techniques pioneered by Quantum. No external
switches, opamps, or other analog components aside from CS are required.
A unique feature is the 'slosh filter', a detection integrator which averages detections over a rolling 15 second
interval before activating or deactivating the OUT pins. This filter allows use of the QT114 with violently moving
fluids, for example in a moving vehicle, that would otherwise cause the outputs to flicker between two states.
The device also includes selectable output polarity, allowing both output lines to be made either active-high or
active-low. It also includes the Quantum-pioneered HeartBeat™ signal, allowing a host controller to monitor the
health of the QT114 continuously if desired. By using the charge transfer principle, the IC delivers a level of
performance clearly superior to older technologies. It is specifically designed to replace electromechanical
devices like float switches, thermistors, and conductance probes.
TA
00C to +700C
-400C to +850C
Quantum Research Group Ltd
AVAILABLE OPTIONS
SOIC
QT114-S
QT114-IS
8-PIN DIP
QT114-D
-
Copyright © 1999 Quantum Research Group Ltd
R1.03







QT114 pdf, 数据表
Figure 3-2
Getting HeartBeat pulses with a pull-down resistor
HeartBeat™ Pulses
2
OUT1
Ro
3
OUT2
Ro
4
FILT
7
SNS2
6
SNS1
5
POL
Figure 3-3
Using a micro to obtain HB pulses in either output state
PORT_M.1
PORT_M.2
Microprocessor PORT_M.3
PORT_M.4
R1
R2
2
OUT1
3
OUT2
4
FILT
7
SNS2
6
SNS1
5
POL
Electromechanical devices will ignore this short pulse. The
pulse also has too low a duty cycle to visibly affect LED’s. It
can be filtered completely if desired, by adding an RC
timeconstant to filter the output, or if interfacing directly and
only to a high-impedance CMOS input, by doing nothing or
at most adding a small non-critical capacitor from each used
OUT line to ground (Figure 3-4).
3.4 ESD PROTECTION
In some installations the QT114 will be protected from direct
static discharge by the insulation of the electrode and the
GATE OR
MICRO INPUT
CMOS
CMOS
100pF
100pF
Co
Co
2
OUT1
3
OUT2
4
FILT
7
SNS2
6
SNS1
5
POL
Figure 3-4 Eliminating HB Pulses
fact that the probe may not be accessible to human contact.
However, even with probe insulation, transients can still flow
into the electrode via induction, or in extreme cases, via
dielectric breakdown. Some moving fluids (like oils) and
powders can build up a substantial triboelectric charge
directly on the probe surface.
The QT114 does have diode protection on its terminals
which can absorb and protect the device from most induced
discharges, up to 20mA; the usefulness of the internal
clamping will depending on the probe insulation's dielectric
properties, thickness, and the rise time of the transients.
ESD dissipation can be aided further with an added diode
protection network as shown in Figure 3-5. Because the
charge and transfer times of the QT114 are relatively long,
the circuit can tolerate very large values of Re1, as much as
50k ohms in most cases without affecting gain. The added
diodes shown (1N4150, BAV99 or equivalent low-C diodes)
will shunt the ESD transients away from the part, and Re1
will current-limit the rest into the QT110's own internal clamp
diodes. C1 should be around 10µF if it is to absorb positive
transients from a human body model standpoint without
rising in value by more than 1 volt. If desired C1 can be
replaced with an appropriate zener diode. Directly placing
semiconductor transient protection devices or MOV's on the
sense lead is not advised; these devices have extremely
large amounts of parasitic C which will swamp the sensor.
Re2 functions to isolate the transient from the QT110's Vcc
pin; values of around 1K ohms are reasonable.
As with all ESD protection networks, it is important that the
transients be led away from the circuit. PCB ground layout is
crucial; the ground connections to the diodes and C1 should
all go back to the power supply ground or preferably, if
available, a chassis ground connected to earth. The currents
should not be allowed to traverse the area directly under the
QT114.
If the QT114 is connected to an external circuit via a long
cable, it is possible for ground-bounce to cause damage to
the OUT pins; even though the transients are led away from
the QT114 itself, the connected signal or power ground line
will act as an inductor, causing a high differential voltage to
build up on the OUT wires with respect to ground. If this is a
possibility, the OUT pins should have a resistance in series
with them on the sensor PCB to limit current; this resistor
should be as large as can be tolerated by the load.
3.5 SAMPLE CAPACITOR
Charge sampler Cs should be a stable grade of capacitor,
like PPS film, NPO ceramic, or polycarbonate. The
acceptable Cs range is anywhere from 10nF to 100nF
(0.1uF) and its required value will depend on load Cx. In
some cases, to achieve the 'right' value, two or more
capacitors may need to be wired in parallel.
Vcc
1
2 OUT1 SNS2 7
3 OUT2 SNS1 6
4 FILT
POL 5
8 Gnd
Re2 C1 10F
Re1 To Electrodes
CS
Figure 3-5 ESD Protection Network
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