Capacitance level measurement circuit and system

ES 2 245 362 T3

DESCRIPTION

Circuit and system for measuring the capacity level.

Background information

This invention relates to capacity measurement probes, and more particularly to a capacity probe and the operational circuitry thereof.

Capacity probes are often used to measure the level of a material in a tank or other compartment. When the material rises into the compartment, it replaces the air between two electrodes or conductors. If the material has a higher dielectric constant than air, the total capacity of the system increases as the compartment fills. This increased capacity provides an indication of the amount of material in the compartment.

In order for the capacity probe to function in this configuration, a pair of conductors must be spaced so that the material to be measured can fill the space between them. If the probe is to be inserted into conductive materials, then it must also incorporate some procedure to electrically isolate the conductors from each other.

A capacitive apparatus, shown in US Patent No. 3,774,238 to Hardway, uses two long tubes or rods 26, 27 insulated from each other in a spaced relationship separated by plastic insulators 28.

Another type of capacitance probe, shown in US Patent No. 5,397,995 to Anderson, includes an outer conductor and a spaced inner conductor. The gap between the conductors insulates the conductors from each other and allows the material to be measured to fill in the gap.

US-A-6 016 697 describes a capacitive level detection system including an elongated capacitive probe positioned vertically within the container so that a lower part of the probe is in the liquid and an upper part of the probe extends above the surface of the liquid. A capacitive liquid reference sensor is close to the lower end of the probe, and a capacitive gas reference sensor is close to the upper end of the probe. A controller controls each of the sensors with an electrical signal and produces a resulting value that corresponds to the capacity of each of the sensors.

Document DE-A-4329571 describes a capacitive AC tilt sensor for determining the level of lubricating dielectric liquid of the transmission of a vehicle that divides the capacitor into two pairs of electrodes spaced by holes in which the liquid is located, the holes of which they communicate by the principle of communicating vessels.

US-A-4 383 444 describes a level measurement system based on the conversion of capacitance to current provided with equipment to compensate for variations in dielectric constant in a measured liquid. A reference probe is located completely within the liquid to be measured. The measurement probe responds both to changes in the dielectric constant and to variations in the liquid level. A differential output of the reference probe and the measurement probe compensates for variations in the dielectric constant in the measured material. A control unit at the output provides a means for automatic calibration via a microprocessor.

A disadvantage of known capacitance probes is their susceptibility to capacitance inaccuracies, commonly known as "stray capacitances", that exist between various components of the capacitance measurement circuit, including the probe itself. Furthermore, these parasitic capacities are often variable, being influenced by ambient temperature and / or ambient humidity. Thus, there is a need for an improved capacitance probe and circuitry therefor.

Summary

According to one embodiment of this invention, a capacity level measurement circuit comprises a control circuit including a power port coupled to a constant current source, a detector port coupled to a threshold detector, a probe port coupled to a probe capacitor, a reference port coupled to a reference capacitor, a plurality of switches that are operable to alternately couple said feed port to the probe port and to said reference port; said control circuit being configured to generate a linear ramp waveform signal having a slope that is proportional to the magnitude of the capacitance of a probe capacitor and a reference capacitor coupled to said probe port and to said probe port. reference; wherein the parasitic capacitance between the reference capacitor and the probe capacitor is substantially eliminated by maintaining the voltage between the plates of said reference capacitor at the same level as in said probe capacitor during the measurement of the capacitance level .

ES 2 245 362 T3

In a variation, the present invention may include a capacity probe that includes this capacity level measurement circuit.

In another aspect, the present invention includes a method of determining the capacity of a level measurement capacity probe. The procedure includes providing a selection / screening control circuit, coupling a constant current source to the selection / screening control circuit, coupling a probe capacitor to the selection / control circuit, coupling a reference capacitor to the selection circuit. / control, and providing a select / control circuit with a plurality of switches that are operable to alternately couple the constant current source to the probe capacitor and the reference capacitor. The method also includes configuring the select / shield control circuit to alternately generate a linear ramp waveform signal having a slope that is proportional to the magnitude of the capacitance of a probe capacitor and a capacitor of reference coupled to said probe port and said reference port, and actuation of the switches to alternately couple the constant current source with the probe capacitor and with the reference capacitor. Select / shield control circuits are used to alternately generate a linear ramp waveform signal having a slope that is proportional to the magnitude of the capacitance of a probe capacitor and a reference capacitor. A voltage differential of substantially zero volts is maintained between the reference capacitor and the probe capacitor during the aforementioned use of the selection / screening control circuit.

Brief description of the drawings

The foregoing and other features and advantages of this invention will be more clearly apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings in which:

Figure 1 is a schematic representation of a capacity probe of the present invention;

Figure 2A is a schematic representation of the measurement circuitry of the present invention useful in operating the capacity probe of Figure 1;

Figure 2B is a schematic representation of the electrical wiring of the capacity probe of Figure 1;

Figure 3 is a schematic representation of a processor used to operate the circuitry of Figure 2A; Y

Figure 4 is a schematic representation of additional and / or optional components coupled to the circuitry of Figures 2A and 3.

Detailed description

With reference to the figures set forth in the accompanying drawings, illustrative embodiments of the present invention will now be described in detail. For clarity of discussion, like features shown in the accompanying drawings will be indicated by like reference numerals and like features shown in alternate embodiments in the drawings will be indicated by like reference numerals.

As shown in Figures 1 and 2A, the invention that is the subject of this document includes a measurement circuit 22 that can be used in combination with a capacity probe 10 to measure the level of a material 12 in a compartment 14. Generally the probe 10 includes a probe condenser 21 (for measuring material level), and a reference condenser (cell) 44 used to calibrate probe condenser 21 for a particular material 12 being measured. Measurement circuit 22 actively compensates for parasitic capacitors that typically exist between probe capacitor 21 and reference cell 44. Circuit 22 performs this functionality by supplying a constant current to probe capacitor 21 at the start of measurement. This constant current generates a voltage across capacitor 21 which is a linear ramp waveform that has a slope that is proportional to the magnitude of the capacitance. A timer measures the elapsed time ("t") between the initiation of the measurement and the time in which the voltage waveform reaches a predetermined level (eg, 2 volts). This time value "t" is proportional to the value of the capacitance of the probe capacitor 21. This parasitic capacitance (ie, between capacitor 21 and cell 44) is actively removed by keeping the voltage across reference cell 44 at the same level as across capacitor 21 during the measurement cycle. By keeping these voltages nominally identical, any difference in voltage between capacitor 21 and cell 44 is substantially eliminated to nominally eliminate this parasitic capacitance. A similar sequence of events is effected for the measurement of the reference cell 44. In this manner, embodiments of the present invention make it possible to perform relatively accurate measurements of the capacities of the probe capacitor 21 and the reference cell 44.

Referring now to Figures 1 through 4, embodiments of the present invention will be described in greater detail. As shown in Figure 1, the invention that is the subject of this document includes a capacity probe 10 for use in measuring the level of (i.e., the depth of insertion of probe 10 within)

ES 2 245 362 T3 a material 12 in a compartment 14. The probe 10 may be of the type set forth in United States Patent Application Serial Number 09 / 696,329, entitled Low Cost Capacity Probe, dated 24 of October 2000. In one particular configuration, the probe 10 was found to have advantages in measuring fuel levels in fuel tanks.

As shown, probe 10 forms a probe capacitor 21 showing a capacity indicated as C_probein Figure 1. As material 12 rises into a compartment (eg, a reservoir) 14, it passes into a space 16 between two electrodes or conductors 18, 20 that are coupled to an electronic module (ie, the circuitry) 22 which is described in greater detail later herein. Air or other gas escapes from space 16 through openings 25 in outer conductor 20 as material 12 rises into space 16. If material 12 has a higher dielectric constant than air, then C_probe The capacity of probe capacitor 21 (i.e., the capacitance between conductors 18, 20), increases as compartment 16 fills. This increase in capacity provides an indication of the amount (i.e., level) of material 12 in compartment 14.

As also shown, the capacitance probe 10 may include a reference cell (i.e., a capacitor) 44 located at a distal end 46 of, and concentrically with, the inner conductor 18. The reference cell 44 functions as a capacitor. relatively small of known size that allows automatic calibration for the dielectric of the particular material 12 in compartment 14. Cell 44 thus nominally eliminates the need to calibrate a measurement in the field and allows the system, ie, probe 10 and circuitry 22, to conveniently compensate for materials 12 of various dielectrics.

Reference cell 44 includes a first reference lead 48 connected using a non-conductive spacer 50 to the distal end 46 of inner lead 18. Both lead 48 of reference cell 44 and lead 18 of capacitor 21 are electrically connected. to circuitry 22 by means of an electrical conductor (eg, a wire) 56 that nominally extends through the center of inner conductor 18.

In operation, the capacity probe 10 is at least partially inserted into a compartment 14 having a material 12 therein. As material 12 in compartment 14 enters space 16 between inner conductor 18 and outer conductor 20, the presence of material 12 serves to alter the electric field between inner and outer conductors 19, 20. Circuitry 22 measures the capacity between the conductors

13, 20 and derives from the capacity measurements a signal proportional to the material level 12 within the aperture 16. The components and operation of the circuitry 22 will be described in greater detail later herein. Since the reference cell 44 is completely submerged within the material 12, its capacity C_ref provides a value for a known level (height) of the material 12. The two capacitors 21 and 44 of probe 10 can thus be used as variable capacitors to measure the level of material in the tank

14.

For example, reference cell 44 may have a predetermined (axial) length 45, such as 1 to 2 inches (about 2.5 to 5 centimeters). The probe capacitor 21 can be of any desired length 23 that represents the range of levels capable of being measured. For many fuel tank applications, the (axial) length 23 typically ranges from 36 to 93 inches (approximately 91.4 to 236.2 centimeters). Circuitry 22 measures C_probeof C_ref over the air and stores these values ​​in memory 100 (for example, a non-volatile memory of an EEPROM device as shown in Figure 4). When probe 10 is immersed in fluid 12 with a different dielectric than air, the C_ref the capacity of the reference cell 44 changes, as does the C_probe of the capacitance of the probe capacitor 21. This change in the capacitance per unit length is measured by means of the circuit 22 and the level can be calculated by means of the microprocessor 200 (figure 3) using the following equation (1):

^Level = C^onst *⁽⁽Csonda ^Cprobe ^ re) / (^Ccell ^ ef cellrefaire

))

Eq. 1

Equation 1 theoretically generates the desired result because reference cell 44 has the same radial dimensions as probe capacitor 21, reference cell 44, and capacitor 21 are both immersed in the same type of fluid 12, and their change in the capacity per unit length is nominally identical. The constant Const in the above equation 1 corresponds to the length 45 (which in this example is 2 inches). Probe 10 is self-calibrating because the dielectric of fluid 12 falls outside the level of Eq. 1, (that is, because equation 1 is radiometric). As such, the level measurement is independent of the dielectric of the fluid, so it can be used in fluids of many types without additional calibration.

One difficulty associated with this configuration is that the wire 56 running from the reference cell 44 to the electronics 22 adds a variable parasitic capacitance, dependent on the temperature shown as C_{little girl}in Figures 1 and 2. This parasitic capacity also varies as the fluid level 12 changes. This capacity can thus generate a relatively large error since the level equation Eq. 1 does not take into account this parasitic term. The circuitry 22 of the present invention advantageously serves to eliminate this potential error.

Circuitry 22 will now be described in greater detail with reference to Figures 2A-2B. Circuitry 22 includes a current source 110, a selection / screening control portion 120, and a threshold detector.

ES 2 245 362 T3

130. As shown in Figure 2B, leads 18 and 56 of probe assembly 10 (Figure 1) connect to terminals 132 and 134, respectively, of control portion 120. Shield 20 of probe 10 is connected to terminal 136 of control part 120.

Referring now in particular to FIG. 2A, specific components of circuitry 22 are described in conjunction with the following functional description. The skilled person will recognize that various components described herein, such as operational amplifiers and voltage references, typically require power supplies which, according to common practice, cannot be explicitly shown in the figures. In the particular embodiment shown and described, the skilled person should recognize that such components can be powered by any suitable power source, such as, for example, a 5.0 volt analog power source referred to in the figures like "VANALOG".

As shown, current source 110 may be a high output impedance current source capable of delivering a constant current of 60 nanoamps (nA) to control portion 120, through output terminal 136. In the embodiment Particularly shown, current source 110 includes an operational amplifier (Amp-Op) 138, and a voltage reference 140 that produces 2.0 volts at terminal 142 relative to terminal 144. Current source 110 also includes capacitors C52, C47, resistors R16, R24, and a capacitor C37. Resistors R24 and R16 serve to divide the reference voltage (2.0 volts) down to approximately 0.6 volts that appear between the terminals of resistor R22. In the particular embodiment shown, resistor R22 has a resistance of nominally 10 megohms (M). The 0.6 volts across the terminals of the 10M resistor draws a current at output 136 of nominally 60 nA.

Current source 110 can be selectively applied to either probe capacitor 21 or reference cell 44, using analog control switches 111-116 120, as discussed later herein. By sequencing these switches, the constant current of 60 nA can be applied respectively to connector terminal 132, terminal 134, or ground.

The sequence of closures of switches 111-116 is controlled by the microcontroller 200 (figure 3) which is coupled through the output port 151 thereof to control the inputs on each analog switch 111116. These control inputs are respectively labeled SW PROBE , SW REFCELL, SW REFCAP, SW DISCH, SW DSR, and SW DSP, and each is coupled to a switch actuator 148. The switch actuators 148 operate in a conventional manner to alternately open and close the switch 111116 connected thereto, in response to signals from the microcontroller 200.

At the beginning of the measurement sequence (also referred to as the "reset" state) switches 111, 112, 113, and 114 are closed and switches 115 and 116 are open. This provides a path to ground through resistor R18 for the 60 nA current source 110, and also serves to ground terminals 134 and 132 to discharge probe capacitor 21 and reference cell 44 (Figure 1 ). In this state, the voltage at terminal 154 of op amp 138 is nominally (within compliance with op amp 138) at zero volts. Since, in the particular embodiment shown, the operational amplifier 138 is a single power device, the voltage is within approximately 20 mV relative to ground. This puts voltage reference terminal 144 140 nominally to ground. (As will be discussed in greater detail later herein, since terminal 154 tracks the voltage at output 136, the voltage at terminal 144 may also increase during measurement of probe capacitor 21. Reference 140 similarly increases the voltage at its terminal 142 to maintain the voltage differential of 2.0 volts between terminals 142 and 144.)

In this "reset" state, current provided by source 110 flows to ground through R18 when switches 111-114 are closed. The probe measurement sequence can now begin with microcontroller 200 closing switches 111, 113, and 116, and opening switches 112, 114, and 115. An operational amplifier 152 that is coupled to switch 115 at terminal 156 thereof, is configured as a voltage follower such that the voltage at terminal 156 is, within the offset voltage of operational amplifier 152, nominally the same as the voltage at terminal 154 of op amp 138. Since op amp 138 is also configured as a voltage follower, the voltage at terminal 154 of op amp 138 is nominally the same as the voltage at output 136. This loop forces the voltage at terminal 154 of op amp 152 to follow the voltage at output 136. Thus, in this "probe measurement" state (that is, with switches 111, 113, and 116 closed, and switches 112, 114, and 115 open), the 60nA current now flows from output 136 to across resistor R21 inside probe capacitor 21 connected to terminal 134.

This current flow forces the voltage across probe capacitor 21 (eg, between terminal 134 and terminal 136) to a linear increase. The closure of switch 116 serves to keep the voltage across reference cell 44 (connected to terminal 132) at the same level as the voltage across probe capacitor 21 (as long as this voltage across the probe capacitor increases). In addition, this voltage level is maintained in cell 44 as long as the current required to charge reference cell 44 is provided by operational amplifier 152 (i.e., at terminal 156 thereof) rather than by the current source of 60 nA 110. Advantageously, this functionality effectively maintains the voltage across C_country (i.e. through

ES 2 245 362 T3 leads 56 and 18 of Figure 1) to zero volts even as the voltage across probe capacitor 21 increases linearly (ie, during the "ramp period"). This active cancellation of the voltage across the C-Parasite effectively prevents any current (i.e., generates a current of zero nA) flowing through C-Parasite 50 so that nominally all of the 60 nA current flows into the capacitor. probe 21. Closure of switch 113 also applies voltage at terminal 156 of op amp 152 to the grounded side of reset switch 114 to similarly nullify any parasitic capacitance generated by switch 114 while switch 114 is open.

Since terminal 136 is connected to ground, the increase in voltage across probe capacitor 21 generates an increase in voltage at terminal 160 of op amp 152 (and at reference terminal 144 140 connected thereto). As previously mentioned herein, since reference 140 generates a constant 2.0 volt differential between terminals 142 and 144, any increase in voltage at terminal 144 will produce a similar voltage increase at terminal 142. This increasing output serves the current flow at terminal 136 at the aforementioned 60 nA during this ramp or this probe measurement period.

The voltage across probe capacitor 21 (for example, as taken at terminal 160) is applied to input terminal 162 of threshold detector 130. This voltage is applied to input terminal 168 of a comparator 170. At the Particular embodiment shown, comparator 170 includes an operational amplifier similar to operational amplifiers 138 and 152, which are operated in the non-feedback mode. Comparator 170 compares the probe voltage at terminal 168 (eg, 2.0 volts) with the output at terminal 172 of a reference source 140 '. (Reference source 140 is substantially similar to reference source 140 described hereinbefore with respect to current source 110.) Resistors R28 and R29 can be used to provide a small amount of positive feedback around the detector. threshold to avoid false triggering due to noise. When the probe voltage at terminal 168 reaches 2.0 volts (that is, the voltage at terminal 168 becomes equal to the voltage at 172), the comparator generates a signal at the comparator output 174 (for For example, output 174 goes to the "high" level state). This signal, sometimes referred to herein as "MEASURED PULSE" is input to a timer (eg, a 16-bit timer) 178 of microcontroller 200 (FIG. 3). The timer 178 measures the time difference "t" between the closing of the switch 111 and the reception of the MEASURED PULSE signal. Using this timing information, the microcontroller 200 can calculate the capacity of the probe from the following equation (2a):

C = It / V

Eq. 2a where, in the particular embodiment shown, I is the current generated by the current source 110 (for example, 60 nA), t is the time difference declared above, and v the threshold voltage supplied by the reference 140 '( for example, 2.0 volts).

Closing switch 113 during the probe measurement process completely nullifies the parasitic capacitance of reset switch 114, which as discussed earlier in this document is used to ground the 60 nA current during the " reset ”. As discussed before, since the current in the probe capacitor 21 is constant and since the time that this current flows inside the capacitor 21 is measured, the resolution of the measurement is constant, regardless of the size of the probe capacitor 21.

Capacity C_ref of the reference cell 44 is measured in a manner that is substantially similar to the measurement of C_probe as discussed previously herein, except that switches 112, 113, and 115 are closed, and switches 111, 114, and 116 are open. In this way, the 60 nA current generated by current source 110 is applied to terminal 132 for reference cell 44, rather than terminal 134 for probe capacitor 21.

Temperature correction

Due to the sensitive nature of the measurement circuitry 22, relatively large changes in ambient temperature (and humidity) can cause measurement errors. These errors are generally the result of temperature-induced displacement voltage drifts in op amps 138, 152, 170, capacitances between various PCB-mounted components, and changes in humidity that affect to the conductivity of the circuit board surface. At these parasitic capacities influenced by temperature and / or humidity (i.e. parasitic capacities other than C_parasitic described hereinbefore) are collectively referred to as "plate parasitic capacities." In order to compensate for these changes as a function of temperature and humidity, a microcontroller 200 can be provided with a computer-readable program code (software) that measures the spurious plate capacities at calibration and stores these values ​​(for example, in an EEPROM 100 of figure 4).

These spurious measurements in the table are performed in substantially the same way as a probe measurement or reference cell measurement with the following exception. During a measurement of the parasitic capacity of the plate,

ES 2 245 362 T3 switches 111 to 116 are configured as previously stated with respect to the measurement of C_probeexcept that switch 111 is open. This forces the 60 nA current to flow into the probe measurement circuitry (without flowing into the probe capacitor 21), to allow the measurement of the stray capacitance of the board associated with the probe measurement circuitry as a function of time and temperature. Similarly, the parasitic capacity associated with the reference cell circuitry is measured as stated earlier herein with respect to the measurement of C_refexcept that switch 112 is open. These real-time values ​​(C_calsonda and C_calref from equation 3) are affected by temperature and humidity and can be measured while the instrument is operating in order to compensate for changes in them. During the measurement cycle, these calibration values, for example, “C_calsonda"And" C_calref”Can be retrieved (for example, from EEPROM 100) and can be used to modify the previously referenced level equation (Eq. 1) to produce the following improved level equation (Eq. 3):

^{Const level}*^(((CCsondaaire probe) Ccalsonda) / ((^Ccellref Ccellularefaire) Ccalref))

Eq. 3

This modified level calculation can advantageously utilize the nominally stored plate parasitic capacitance calibration values ​​each time a level calculation is performed for improved measurement accuracy. In the event that these parasitic values ​​change as a function of temperature and / or humidity, this modified level equation (Eq. 3) provides a real-time temperature correction term. The sample software used to carry out this function is included in the Appendix attached to this document.

In the particular embodiment shown in figures 3 and 4, the microprocessor 200 can function as a "slave" processor coupled through an interface port 180 (figure 3) to port 182 of a "master" microprocessor 210 (figure 4) . As also shown, EEPROM 100 is directly coupled to microprocessor 210. In this configuration, the "master" microprocessor 210 can provide power to the slave processor 200, a clock pulse, and access to the EEPROM 100. The master microprocessor 210 can also control a wireless module (eg, an ASIC). 220 configured to enable probe 10 to operate wirelessly via radio frequency or other wireless means. Those skilled will recognize that in alternate embodiments, the present invention can be configured without dual Master / Slave processors and / or without wireless capability. For example, a single processor 200 can be used, having the EEPROM 100 or other memory storage device directly coupled thereto, with or without a wireless module 220.

In the above specification, the invention has been described with reference to specific exemplary embodiments. It will be apparent that various modifications and changes can be made thereto without departing from the scope of the invention as stated in the claims which follow. The specification and drawings will be in accordance therewith, considered in an illustrative rather than restrictive sense.

(Scheme goes to next page)

ES 2 245 362 T3

Appendix - Program Code Listing / ****************************************** **************** *

* Project: Centeron * Pile Description: This file contains functions * to pierce the measurements.

* * $ Archive s $ * $ Workfiles $ * $ Revision: $ * $ Date: $ *

*********************************************************** *

* $ History: $ *

************************************************** *********************************************** # include <pic.h>

#include app.h #include cmd.h #define READPROBE #define RFADPROBEAIR idefine READREFCELL

ObOOOlOlOO

ObOOOlOOOO

ObOOOOlOlO #define READREFCELLAIR ObOOOOOOlO #define MAXTIMEROVERFLO 10 #define NÜMBEROFREPEATS 128 #define BADMEASVAL ttdefine H2OLIMIT

99999

775 #define 0PENRATI0 0.6 extern void TimeDelay (unsigned int wMaxCount); extern unsigned char bDumnty; extern unsigned int wDummy; extern unsigned long ulDummy;

unsigned long ulMeasurement;

ES 2 245 362 T3 // ******************************************* **************** // MODULE // AUTHOR // DESCRIPTION // LIMITATIONS // INPUTS // OUTPUTS: measurement value // REVISION HISTORY s // Rev # Yam Date // ........-...................

: Measure: Steve Tymoszuk: Punetion to performed the desired easurement. : none: wSwSet - - measurement mask

Reason // 1 Steve Tymoszuk 24 March 2000

Original // *********************************************** ***************** ****** * * / unsigned long Measure (unsigned int wSwSet) {

unsigned long ulResult;

unsigned char bTemp;

wTimerOverFlow counter an input

Output

Outputs

T1C0N 0x00;

TMR1IF 0x0;

PIE1 = 0x1; for timerl Overflow

INTCON 0x0; for timerl Overflow

CCP1CON ObOO000101;

0; // Clear timer Over flow // Timer 1 Off.

TRISC | = 0x04; // make RC2 / ccpl

TRISO & = OxFE; // make RC0 an

TRISB & = OxEO; // make RB0-RB4 // Olear timerl Overflow flag // Disable all interrupts except // Disable all interrupts except // setup ccpl for no prescaler

ES 2 245 362 T3 ie. every rising edge

TMR1L 0x0; // olear low byte of timerl

TMR1H = 0x0; // olear high byte of timerl

CCP1IF 0x0; // olear ccpl event flag

PEIE 1;

GIE = ​​0x1;

(for timerl Overflow 0NLY) bTemp = PORTB & OxCO;

bTemp = bTemp | ObOOOOllOl;

// Interrupt enable // enable global interrupts

PORTB = bTemp; // Start integrate cycle.

I tested

TimeDelay (100);

// Wait a spell bTemp = PORTB & OxCO; bTemp = bTemp | wSwSet;

PORTB bTemp; integrate cycle.

// Start probe

P0RTC = 0x01;

TiCON 0x01; // Start Timerl while (¡CCP1IF) // Wait for

CCP1 event flag.

/ * wait * /

CCP1IF = 0X00; T1C0N =

0x00; // Stop Timerl ulResult = ((unsigned long) CCPR1H << 8);

ulResult + = (unsigned long) CCPR1L;

ulResult + = ((unsigned long) wTimerOverFlow << 16);

if (wTimerOverFlow> = (MAXTIMEROVERFLO - 1)) {

ES 2 245 362 T3

<img file="ES2245362T3_D0001.tif" />

ES 2 245 362 T3 // 1 Steve Tymoazuk 24 March 2000

Original // *********************************************** ***************** * ♦ ** / unsigned char MeasureProbe (void) {

unsigned char bCnt; unsigned char bResult;

bResult = MEASOK; ulAveprobe = 0;

// Read Probe only.

for (bCnt = 0; bCnt &lt;NUMBEROFREPEATS; bCnt ++) {

ulMeasurement = Measure (READPROBE); ulAveprobe + = ulMeasurement;

if ((float) ulMeasurement &lt;= ((float) wCalProbe * OPENRATIO)

{return (MEASOPENPROBEFLT);

} if (ulMeasurement = BADMEASVAL) {

return (MEASSH0RTPR0BEFLT);

} / * Throw the dog a bone * /

ES 2 245 362 T3

HitWDO;

ReadDataFrom62 ();

} / * calculate the average * / ulAveprObe = ulAveprobe / NUMBEROFRBPEATS; TimeDelay (1);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 ();

return (bResult);

} // ********************************************** ***************** ** / // MODULE // AUTHOR // DESCRIPTION probe board measurement. // LIMITATIONS // INPUTS // OUTPUTS // REVISION HISTORY ¡// Rev # Yam // .........

: MeasureProbeAir: Steve TymOszuk: Function to pierce an averaged: none: none: none

Date Reason // 1 Steve Tymoszuk 24 March 2000

Original // *********************************************** ***************** ** ** / void MeasureProbeAir (void) {

unsignad char bCnt;

ulAveprobeair = 0;

ES 2 245 362 T3 for (bCnt 0; bCnt &lt;NOMBEROFREPEATS; bCnt ++) {

ulAveprobeair + - = Measure (READPROBEAIR);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 ();

/ * calculate the average * / ulAveprobeair = ulAveprobeair / NOMBEROFREPEATS; TimeDelay (1);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 ();

// ** // // AUTHOR // DESCRIPTION measurement.

// LIMITATIONS // INPUTS // OUTPUTS // REVISION HISTORY / / Rev # // ........

MODULE: MeasureRef: Steve Tymoszuk: Function to perfora an averaged ref cell none none none

Yam

Date Reason // 1 Steve Tymoszuk 24 March 2000

Original // *********************************************** ***************** ★ ★ ** /

ES 2 245 362 T3 unsigned char MeasureRef (void) {

unsigned char bCnt; unsigned char bResult;

bResult MEASOK; ulAveref = 0;

// Read Ref cell only.

for (bCnt = 0; bCnt &lt;NUMBEROFREPEATS; bCnt ++) {

ulMeasurement = Measure (READREFCELL);

if ((float) ulMeasurement &lt;= ((float) wCalRef * OPENRATIO))

{return (MEASOPENREFFLT);

} if (ulMeasurement == BADMEASVAL) {

return (MEAS_SHORTREFFLT);

} ulAveref + = ulMeasurement;

/ * Throw the dog a bone * /

HitWO;

ReadDataFrom62 ();

} / * calculate the average * / ulAveref = ulAveref / NUMBEROFREPEATS;

TimeDelayC (1);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 ();

if ((ulAveref &lt;(unsigned long) wCalRef) {

return (MEASMEASFLT);

}

ES 2 245 362 T3 if (H20_PIN == HI)}

if ((ulAveref (unsigned long) wCalRef)) {

if ((ulAveref - (unsigned long) wCalRef)&gt; = H20LIMIT) {bResult = MEAS_H20;

} }

} return (bResult);

} // ********************************************** ***************** * * ** // MODULE s MeasureRefAir // AUTHOR: Steve Tymoszuk // DESCRIPTION: Function to perform an averaged ref cell air measurement.

// LIMITATIONS: none // INPUTS: none // OUTPUTS: none // REVISION HISTORY:

// Rev # Yam Date Reason // ------ -.................................. ...-......

// 1 Steve Tymoszuk 24 March 2000

Original // *********************************************** ***************** ** ** / void MeasureRefAir (void) {

unsigned char bCnt;

ulAverefair = 0;

for (bCnt = 0; bCnt &lt;NUMBEROFREPEATS; bCnt ++) {

ES 2 245 362 T3 ulAverefair + = Measure (READREFCELLAIR);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 ();

} / * calculate the average * / ulAverefair = ulAverefair / NUMBEROFREPEATSj TimeDelay (1);

/ * Throw the dog a bone * /

HitWDO;

ReadDataFrom62 (), ·}

/*************************************************************** * * * *

* Project: Centeron * File Description: This file contains mise.

* functions used in the RF Cap monitor.

* $ Archive: $ * $ Workfile: $ * $ Revisions $ * $ Date: $ ******************************* ********************************* ** *

* $ History: $ *

************************************************** ************** ** / #include app.h #define CPROBECAL (float) (wCalProbe wCalProbeBoard) #define CREFCAL (float) (wCalRef wCalRefBoard) #define MINDIELECTRIC 120,0 //

ES 2 245 362 T3 ********************************************* ******************* * *

<td colspan="2" rowspan="2">** // // AUTHOR</td><td colspan="2">MODULE: TimeDelay</td>

<td rowspan="2"> •</td><td rowspan="2">Steve Tymoszuk General purpose delay routine.</td>

<td> //</td><td>DESCRIPTION</td>

<td> //</td><td>LIMITATIONS</td><td></td><td>none</td>

<td> //</td><td>INPUTS</td><td>s</td><td>unsigned int wMaxCount</td>

<td> //</td><td>OUTPUTS</td><td>s</td><td>none</td>

<td> //</td><td>HISTORY REVIEW</td><td></td><td></td>

// Rev # Yam Date Reason // ...... -..................................

// 1 Steve Tymoszuk March 15, 2000

Original // *********************************************** ***************** * * ** / void TimeDelay (unsigned int wMaxCount) {

unsigned int wCnt;

/ * waste some time * / for (wCnt = 0; wCnt &lt;wMaxCount; wCnt ++);

} // *********************************************** ***************** * * // // AUTHOR // DESCRIPTION auto cal

MODULE: CalcAutCalLevel: Steve Tymoszuk: Punctio to perform the level calculation for

<td> //</td><td></td><td></td><td>probe.</td><td></td>

<td></td><td> //</td><td></td><td>LIMITATIONS: none</td><td></td>

<td> //</td><td>INPUTS</td><td></td><td>: none</td><td></td>

<td> //</td><td>OUTPUTS</td><td></td><td>: none</td><td></td>

<td> //</td><td>REVISION</td><td>HISTORY</td><td></td><td></td>

<td></td><td> //</td><td>Rev #</td><td>Yam</td><td>Date Reason</td>

<td></td><td> //----</td><td></td><td></td><td></td>

ES 2 245 362 T3 // 1 Steve Tymoszuk 15 March 2000

Original // *********************************************** ***************** ** ** / void CalcAutoCalLevel (void) {

/ * Do calculations for actual length * / / * Temperature compensated level computations * / flDenom = ((float) ulAveref - (float) ulAverefair - ς (float) CREFCAL;

if (flDenom&gt; MINDIELECTRIC) {

flNumer = ((float) ulAveprobe - (float) ulAveprobeair) - (float) CPROBECAL;

flLevel = flSpanCal * (flNumer / flDenom);

} else {

flLevel = 0;

{if (flLevel &lt;0,1) {

flLevel = 0;

} flLevel flLevel * 10;

if (wProbeLength &lt;(unsigned int) flLevel) {

wAir = 0;

} else {

wAir = wProbeLength - (unsigned int) flLevel;

// wAir = (unsigned int) flbevel;

} }

ES 2 245 362 T3 // ★ * ★ ** ★★ * ★★ * ★ ** ★ * ★★★ * ♦ ★ * ♦ ★ *** ★ ** ★★ * ★ * ★ ****** * ★ * ★★★ *** ★ * ★★ ♦ * ★★ *** ★ ** ♦ *

<td></td><td> //</td><td>MODULE: Calc2PtLevel</td><td></td>

<td></td><td>// AUTHOR</td><td>: Steve Tymoszuk</td><td></td>

<td> //</td><td>DESCRIPTION</td><td>: Function to pierce the</td><td>level calculation for 2</td>

<td>pt</td><td></td><td></td><td></td>

<td> //</td><td></td><td>probe.</td><td></td>

<td></td><td> //</td><td>LIMITATIONS: none</td><td></td>

<td> //</td><td>INPUTS</td><td>: none</td><td></td>

<td> //</td><td>OUTPUTS</td><td>: none</td><td></td>

<td> //</td><td>HISTORY REVIEW</td><td>s</td><td></td>

<td></td><td>// Rev # //.....-</td><td>Yam</td><td>Date Reason</td>

// 1 Steve Tymoszuk March 15, 2000

Original // *********************************************** ***************** ** ** / void Calc2PtLevel (void) {

flDenom = ((float) ulCapHi - (float) ulCapLo);

if (flDenOm &lt;= 0) {

wAir 9999;

} else {

flNumer = ((float) wLevHi - (float) wLevLo);

if (ulAveprobe &lt;ulCapLo) {

wAir = wProbeLength;

} else {

if ((ulAveprobe - ulCapLo)&gt; (ulCapHi - ulCapLo))

ES 2 245 362 T3 {

wAir = 0;

} else {

flLevel = (ulAveprobe - ulCapLo) * (flNumer / flDenom);

flLevel = flLevel + (float) wLevLo;

if ((unsigned int) flLevel&gt; wProbeLength) {

wAir = 0;

} else {

wAir wProbeLength - (unsigned int) flLevel;

} }

} }

}

Having thus described the invention, what is claimed is.