WO2017190303A1

WO2017190303A1 - Total dissolved solid sensor with dynamic gain

Info

Publication number: WO2017190303A1
Application number: PCT/CN2016/081092
Authority: WO
Inventors: Yubin LV; Bo REN; Junfeng Wang
Original assignee: Honeywell International Inc.
Priority date: 2016-05-05
Filing date: 2016-05-05
Publication date: 2017-11-09

Abstract

A method includes operations of measuring total dissolved solids (TDS) in a liquid sample to provide a measurement signal, amplifying the measurement signal using a programmable gain amplifier to provide an amplified signal representative of the measurement, converting the amplified signal to a digital signal, if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier and repeating the measuring and amplifying operations, and responsive to the digital signal being within the adjustment range, calculating a result signal based on the digital signal, the result signal being indicative of a concentration of the TDS.

Description

Total Dissolved Solid Sensor with Dynamic Gain

Background

Existing low cost total dissolved solids (TDS) sensors suffer from low performance on accuracy, with substantial deviations, even when measuring dissolved solids in the 1 to 250 ppm (parts per million) range.

Summary

A machine readable storage device has instructions for execution by a processor of the machine to perform operations. The operations include obtaining a measurement sample representative of total dissolved solids (TDS) in a liquid sample, setting a gain of a programmable gain amplifier to provide an amplified signal representative of the measurement, obtaining a digital signal representative of the amplified signal, if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier, and responsive to the digital signal being within the adjustment range, calculating a result signal based on the digital signal, the result signal being indicative of a concentration of the TDS

A device includes an adjustable gain amplifier coupled to receive and amplify a total dissolved solid (TDS) sensor analog signal representative of TDS in a sample. An analog to digital converter is coupled to convert the analog signal to a digital signal. A circuit is coupled to receive the digital signal, compare the digital signal to an acceptable range of digital signals, adjust the gain of the adjustable amplifier if the digital signal is outside the acceptable range of digital signals, and calculate an output signal representative of TDS if the digital signal is within the acceptable range of digital signals.

Brief Description of the Drawings

FIG. 1 is a block diagram of a system for processing a total dissolved solid (TDS) sensor signal according to an example embodiment.

FIG. 2 is a flowchart illustrating a method of processing a TDS sensor signals according to an example embodiment.

FIGs. 3A, 3B, 3C, 3D, and 3E are a set of curves illustrating segmentation of calibration curves for calculating a TDS value from the sensor signal according to an example embodiment.

FIG. 4 is a block diagram of circuitry for performing methods according to example embodiments.

Detailed Description

In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.

The functions or algorithms described herein may be implemented in software in one embodiment. The software may consist of computer executable instructions stored on computer readable media or computer readable storage device such as one or more non-transitory memories or other type of hardware based storage devices, either local or networked. Further, such functions correspond to modules, which may be software, hardware, firmware or any combination thereof. Multiple functions may be performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server or other computer system, turning such computer system into a specifically programmed machine.

FIG. 1 is a block diagram of a system 100 for processing a total dissolved solid (TDS) sensor signal according to an example embodiment. System 100 uses a TDS sensor 110 to sense TDS in a liquid 115 by measuring the electrical conductivity of the solution and then converting the measured conductivity to an amount of TDS in PPM (parts per million) . The sensor 110 may be in the shape of a water tester pen with two

electrodes

117, 118, and provides an analog representation of the TDS represented at 120 to a programmable gain adjustment (PGA) circuit 125. The sensor 110 may also be a probe with the two electrodes fixed by a plastic housing. The PGA circuit 125 in one embodiment has a gain that is adjustable from for example, 1 to 10. The ranges of available gains may vary in further embodiments. The PGA circuit 125, in one embodiment, provides an analog signal 127 representative of the analog signal 120.

In some examples, the sensed analog signal 120 may be a voltage that is amplified by the PGA circuit 125. If the sensed analog signal 120 is low and the gain is also low, the amplified analog signal 127 that is provided to an analog to digital, A/D converter 130 may be below a low value, that is below an ideal range of the A/D converter 130, resulting in a less accurate digital signal 132. In some embodiments, the A/D converter 130 may have an 8 bit output, and a range of 0 volts to 3 volts. An ideal value for conversion may be around 2.5 volts.

The digital signal 132 is provided to a gain adjust circuit 135, which in some embodiments may be a microprocessor executing program code designed to determine a gain value 140 for the PGA 125 responsive to the digital signal 132. In one embodiment, if the digital signal is above a high value of an acceptable value of a range of digital values, the gain is calculated to be a minimum gain of the PGA 125. The measurement is then repeated and amplified using the minimum gain. The minimum gain will likely result in a digital signal 132 that is below a low value of the acceptable range. In one embodiment, the gain is calculated to result in an amplified voltage 127 that is near an optimal value for the A/D converter 130. For example, if the voltage 120 is 0.2 volts, and the optimum value of the A/D converter 130 is 2.5 volts, the gain may be set to 10, and the measurement repeated. The gain of 10 will result in a measurement of 0.2 volts being amplified 10x, resulting in a 2.0 volt signal being provided to the A/D converter 130. The gain may alternatively be set to 12.5x if within the adjustment range of the PGA, resulting in a 2.5 volt signal being provided to the A/D converter 130.

In some embodiments, the initial gain of the PGA may be set to a lowest value, such as 1, which may provide the ability to accurately adjust the gain after one measurement. In further embodiments, a higher gain may be used for an initial measurement, with the gain for successive measurements being reduced by a set amount or percentage in an iterative manner until the amplified voltage 127 is within the low and high voltages values of an acceptable range.

The ability to modify the gain allows the user of a lower cost A/D converter with only 8 bit resolution without sacrificing accuracy. The PGA 125 and gain adjust circuit 135 are also fairly low cost in comparison with higher accuracy, larger range A/D converters. Higher resolution A/D converters may also be used in further embodiments with acceptable ranges being adjusted accordingly. The acceptable ranges in some embodiments are dependent on the A/D converter used, as different A/D converters may have different acceptable ranges and different resolutions.

FIG. 2 is a flowchart illustrating a method 200 of processing TDS sensor signals according to an example embodiment. At 210, a TDS sensor is used to measure a concentration of a dissolved solid in a solution. The measurement in one embodiment is a voltage that is amplified and converted to a digital signal at 220. At 230, a check is made to determine if the digital signal is out of range. In other words, the digital signal may be representative of a voltage that is below a low range value, or may be above a voltage that is above a high range value. The low range value and high range value define a range that is acceptable for the A/D converter. In other words, digital values that are within the range have been found to be more accurate representations of the measured and amplified voltage. Those above the range may max out the resolution of the A/D converter, resulting in the highest digital value that may be provided. At that point, it cannot be determined how far above the high range value that the amplified signal is. If below the low range value, the accuracy of the A/D converter is reduced with respect to the measured signal by the sensor.

If the signal is out of range at 230, the gain for amplifying the measured signal is adjusted. If the signal is below the low value, a simple mathematical calculation may be performed such that a second measured value at 210 that is close to the first measured value will result in an amplified signal whose A/D conversion with within the range. In one embodiment, the calculation is done to make the amplified signal result in an optimum value A/D output, which in one embodiment is representative of a 2.5 volt amplified signal.

If the signal is above the high value of the range, the gain may be reduced for the next measurement at 210. One simple way to adjust the gain may be to reduce the gain to a minimum value, such as 1. A gain of 1 will likely result in a measured amplified signal that results in an A/D output that is below the low value of the range. One further iteration of measurement may then be performed, using a gain value that is calculated to result in an optimum A/D output. In further embodiments, the gain may be reduced by a set amount or percentage, or other value through multiple iterations until the A/D output is within the range.

FIGs. 3A, 3B, 3C, 3D, and 3E are a set of curves illustrating segmentation of calibration curves for calculating a TDS value from the sensor signal according to an example embodiment. At 310, a single calibration curve for a range of 0-2000 for the output of the A/D converter shown on the X-axis, with a TDS value in part per million (ppm) shown as the Y-axis. In some embodiments, the Y-axis may instead represent an interim value that may be used in conjunction with temperature compensation to calculate the TDS. Note that all curves in FIG. 3 represent the A/D converter output on the X-axis and corresponding ppm on the Y- axis. The curve illustrated at 310 is a third order polynomial curve for an entire range of the A/D converter. Measured data points from a very accurate TDS sensor are shown as circles on the curve, with the curve from the polynomial represented as dots. The polynomial equation may be determined using common curve fitting techniques.

A fourth order polynomial curve is shown at 320. As seen, the curve 320 fits the accurate measurements more closely than the curve in 310, but consumes additional computing resources to calculate. Curve 320 also extends over the entire output range of the A/D converter. Of note is that the

curves

310 and 320 both become very steep once the output of the A/D converter reaches 1500. This can result in a loss of resolution, since small changes of the A/D output result in wider swings in the ppm of the TDS value.

Curves

330, 340, and 350 illustrate a segmentation of the curves over different ranges of A/D output, which can improve the calibration accuracy even when compared to higher order single range polynomials. Separate third order polynomials may be determined using known curve fitting techniques. Curve 330 corresponds to A/D outputs between 0-250, curve 340 corresponds to A/D outputs between 200-600, and curve 350 corresponds to A/D outputs between 500-2000.

Note that in one embodiment, several of the curves overlap. For instance, curve 330 covers 0-250 and curve 240 covers 200-600. These curves overlap from 200-250. Both curves may be used in one embodiment for calculating TDS from A/D outputs in the range of 200-250, averaging the results from each to obtain an output value. Similarly the overlap of the ranges of

curves

340 and 350, from 500-600 may also be averaged to determine the output value.

FIG. 4 is a block diagram of circuitry 400 for performing methods according to example embodiments. All components need not be used in various embodiments, as the circuitry may most likely be implemented as a programmed microprocessor or application specific integrated circuit, and may include the A/D converter in some embodiments. One example computing device in the form of a computer 400 may include a processing unit 402, memory 403, removable storage 410, and non-removable storage 412. Although the example computing device is illustrated and described as computer 400, the computing device may be in different forms in different embodiments. For example, the computing device may instead be a smartphone, a tablet, smartwatch, or other computing device including the same or similar elements as illustrated and described with regard to FIG. 4. Devices such as smartphones, tablets, and smartwatches are generally collectively referred to as mobile devices. Further, although the various data storage elements are illustrated as part of the computer 400, the storage may also or alternatively include cloud-based storage accessible via a network, such as the Internet.

Memory 403 may include volatile memory 414 and non-volatile memory 408. Computer 400 may include –or have access to a computing environment that includes –a variety of computer-readable media, such as volatile memory 414 and non-volatile memory 408, removable storage 410 and non-removable storage 412. Computer storage includes random access memory (RAM) , read only memory (ROM) , erasable programmable read-only memory (EPROM) & electrically erasable programmable read-only memory (EEPROM) , flash memory or other memory technologies, compact disc read-only memory (CD ROM) , Digital Versatile Disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices capable of storing computer-readable instructions for execution to perform functions described herein.

Computer 400 may include or have access to a computing environment that includes input 406, output 404, and a communication connection 416. Output 404 may include a display device, such as a touchscreen, that also may serve as an input device. The input 406 may include one or more of a touchscreen, touchpad, mouse, keyboard, camera, one or more device-specific buttons, one or more sensors integrated within or coupled via wired or wireless data connections to the computer 400, and other input devices. The computer may operate in a networked environment using a communication connection to connect to one or more remote computers, such as database servers, including cloud based servers and storage. The remote computer may include a personal computer (PC) , server, router, network PC, a peer device or other common network node, or the like. The communication connection may include a Local Area Network (LAN) , a Wide Area Network (WAN) , cellular, WiFi, Bluetooth, or other networks.

Computer-readable instructions stored on a computer-readable storage device are executable by the processing unit 402 of the computer 400. A hard drive, CD-ROM, and RAM are some examples of articles including a non-transitory computer-readable medium such as a storage device. The terms computer-readable medium and storage device do not include carrier waves. For example, a computer program 418 capable of providing a generic technique to perform access control check for data access and/or for doing an operation on one of the servers in a component object model (COM) based system may be included on a CD-ROM and loaded from the CD-ROM to a hard drive. The computer-readable instructions allow computer 400 to provide generic access controls in a COM based computer network system having multiple users and servers.

Examples:

1. A method including operations comprising:

measuring total dissolved solids (TDS) in a liquid sample to provide a measurement signal；

amplifying the measurement signal using a programmable gain amplifier to provide an amplified signal representative of the measurement；

converting the amplified signal to a digital signal；

if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier and repeating the measuring and amplifying operations； and

responsive to the digital signal being within the adjustment range, calculating a result signal based on the digital signal, the result signal being indicative of a concentration of the TDS.

2. The method of example 1 wherein the measurement signal comprises an analog signal, and an analog to digital converter converts the analog signal to the first digital signal.

3. The method of any of examples 1-2 wherein the result signal is calculated using a programmed microprocessor.

4. The method of any of examples 1-3 wherein the result signal comprises a parts million representation of the TDS in the liquid sample.

5. The method of any of examples 1-4 wherein the TDS comprises a salt.

6. The method of any of examples 1-5 wherein the gain of the adjustable gain programmable amplifier is adjusted a first time to a minimum value.

7. The method of any of examples 1-6 wherein the gain of the adjustable gain programmable amplifier is adjusted from the minimum value to a calculated value.

8. The method of example 7 wherein the calculated value is determined via a table or by calculation using a polynomial calibration equation.

9. A machine readable storage device having instructions for execution by a processor of the machine to perform:

obtaining a measurement sample representative of total dissolved solids (TDS) in a liquid sample；

setting a gain of a programmable gain amplifier to provide an amplified signal representative of the measurement；

obtaining a digital signal representative of the amplified signal；

if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier； and

10. The machine readable storage device of example 9 wherein the measurement signal comprises an analog signal, and an analog to digital converter converts the analog signal to the first digital signal.

11. The machine readable storage device of any of examples 9-10 wherein the result signal comprises a parts million representation of the TDS in the liquid sample.

12. The method of any of examples 9-11 wherein the gain of the adjustable gain programmable amplifier is adjusted a first time to a minimum value and wherein the gain of the adjustable gain programmable amplifier is adjusted from the minimum value to a calculated value.

13. A device comprising:

an adjustable gain amplifier coupled to receive and amplify a total dissolved solid (TDS) sensor analog signal representative of TDS in a sample；

an analog to digital converter coupled to convert the analog signal to a digital signal； and

a circuit coupled to receive the digital signal, compare the digital signal to an acceptable range of digital signals, adjust the gain of the adjustable amplifier if the digital signals is outside the acceptable range of digital signals； and calculate an output signal representative of TDS if the digital signal is within the acceptable range of digital signals.

14. The device of example 13 wherein the analog to digital converter has an output of eight bits.

15. The device of any of examples 13-14 wherein the acceptable range of digital signal comprises values corresponding to an amplified analog signal of between a low value of the range and a high value of the range.

16. The device of example 15 wherein the low value of the range comprises 2 and the high value of the range comprises 2.5 volts.

17. The device of any of examples 15-16 wherein the circuit adjusts the gain to a minimum gain value of the adjustable gain amplifier responsive to the high value of the range being exceeded.

18. The device of any of examples 15-17 wherein the circuit adjusts the gain responsive to the low value of the range not being reached, wherein the adjustment is based on a table lookup or execution of an algorithm.

19. The device of any of examples 13-18 wherein the output signal representative of the TDS is calculated by the circuit in accordance with a polynomial calibration curve.

20. The device of example 19 wherein the polynomial calibration curve comprises multiple overlapping calibration curves, and wherein values from two overlapping curves are averaged where such curves overlap to calculate the output signal.

Although a few embodiments have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Other embodiments may be within the scope of the following claims.

Claims

A method including operations comprising:

measuring total dissolved solids (TDS) in a liquid sample to provide a measurement signal；

amplifying the measurement signal using a programmable gain amplifier to provide an amplified signal representative of the measurement；

converting the amplified signal to a digital signal；

if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier and repeating the measuring and amplifying operations； and

responsive to the digital signal being within the adjustment range, calculating a result signal based on the digital signal, the result signal being indicative of a concentration of the TDS.
The method of claim 1 wherein the measurement signal comprises an analog signal, and an analog to digital converter converts the analog signal to the first digital signal.
The method of claim 1 wherein the result signal comprises a parts million representation of the TDS in the liquid sample.
The method of claim 1 wherein the gain of the adjustable gain programmable amplifier is adjusted a first time to a minimum value and wherein the gain of the adjustable gain programmable amplifier is adjusted from the minimum value to a calculated value.
A machine readable storage device having instructions for execution by a processor of the machine to perform:

obtaining a measurement sample representative of total dissolved solids (TDS) in a liquid sample；

setting a gain of a programmable gain amplifier to provide an amplified signal representative of the measurement；

obtaining a digital signal representative of the amplified signal；

if the digital signal is outside an adjustment range, adjusting the gain of the programmable gain amplifier； and

responsive to the digital signal being within the adjustment range, calculating a result signal based on the digital signal, the result signal being indicative of a concentration of the TDS.
The machine readable storage device of claim 5 wherein the measurement signal comprises an analog signal, and an analog to digital converter converts the analog signal to the first digital signal.
The machine readable storage device of claim 5 wherein the result signal comprises a parts million representation of the TDS in the liquid sample and wherein the gain of the adjustable gain programmable amplifier is adjusted a first time to a minimum value and wherein the gain of the adjustable gain programmable amplifier is adjusted from the minimum value to a calculated value.
A device comprising:

an adjustable gain amplifier coupled to receive and amplify a total dissolved solid (TDS) sensor analog signal representative of TDS in a sample；

an analog to digital converter coupled to convert the analog signal to a digital signal； and

a circuit coupled to receive the digital signal, compare the digital signal to an acceptable range of digital signals, adjust the gain of the adjustable amplifier if the digital signals is outside the acceptable range of digital signals； and calculate an output signal representative of TDS if the digital signal is within the acceptable range of digital signals.
The device of claim 8 wherein the acceptable range of digital signal comprises values corresponding to an amplified analog signal of between a low value of the range and a high value of the range and wherein the circuit adjusts the gain to a minimum gain value of the adjustable gain amplifier responsive to the high value of the range being exceeded.
The device of claim 15 wherein the analog to digital converter has a digital output of 8 bits and wherein the low value of the range comprises 2.0 volts and the high value of the range comprises 2.5 volts.