The ADuCM360_demo_cn0411 is a Total Dissolved Solids (TDS) measurements demo project, for the EVAL-ADICUP360 base board with additional EVAL-CN0411-ARDZ shield, created using the GNU ARM Eclipse Plug-ins in Eclipse environment.
The ADuCM360_demo_cn0411 project uses the EVAL-CN0411-ARDZ shield which is a single supply, low power, high precision complete solution for Total Dissolved Solids measurements, including temperature compensation. The circuit is optimized for conductivity measurements used to determine the TDS values, using conductivity cells with BNC plug.
The circuit is divided into three independent measurement front ends: TDS, conductivity and temperature. After signal conditioning, the three channels share an AD7124-8, 24-bit sigma-delta (Σ-Δ) ADC. The AD7124-8, is a low power, low noise, completely integrated analog front end for high precision measurement applications.
For temperature compensation can be used an RTD PT100 sensor, 2-wire.
The ADuCM360_demo_cn0411 application processes ADC outputs for all 5 channels (RTD, Vpeak+ and Vpeak-, VDAC, VR20S, VR200S), calculates conductivity and TDS values using as input RTD temperature value and the peak-to-peak voltage. Those data are sent to serial interface, using UART communication (115200 baud rate and 8-bits data length). The 24-bits ADC data are received using SPI interface of the EVAL-ADICUP360 board.
The temperature value is calculated based on the RTD resistance:
Rrtd = (CODE* Rref) / (2^24 -1) Rref - Reference resistor (4.02kΩ) CODE - ADC output
1. RTD resistance > 100Ω
2. RTD resistance ≤ 100Ω
In order to compute the total dissolved solids parameter a premeasurement procedure is run in the first place that aims to select the proper gain resistance for the measurement.
The multiplexer is set to the highest gain resistance (20MΩ) and the DAC output to a value set by the user (initially set to 400mV). Then, the positive and negative input voltage are captured via ADC channel 1 and 2. If the following formula is met:
Vp = positive input voltage Vp + Vn > 0.3 * 2 * Vexc Vn = negative input voltage Vexc = DAC output voltage
The excitation voltage used for computing tds is set to:
Vexc = 0.4 * Vexc / (Vp + Vn)
Otherwise, the gain resistor is dropped by 1 decade and the premeasurement process is repeated.
After the process is finished, the peak-to-peak voltage is measured again an the peak-to-peak current is computed:
Ipp = peak-to-peak current Ipp = (2 * Vexc - (Vp + Vn)) / Rgain Vexc = excitation voltage computed in the premeasurement procedure Vp = positive input voltage Vn = negative input voltage Rgain = gain resistor set via multiplexer
Based on the peak-to-peak current the electrical conductance is computed, also removing the offset resistance (optional) that is obtained via the software command “refres” found in the list of available commands :
g = Ipp / ((Vp + Vn) - (Ipp * Roff)) Roff = offset resistance g = electrical conductance
The electrical conductivity is computed using the conductance and the cell constant which can be set accordingly for low conductivities, normal conductivities and high conductivities via software commands. A temperature compensation is also performed taking into account the temperature measured via RTD resistance.
s = electrical conductivity s = k * g s_cal = temperature compensated electrical conductivity temp_coeff = solution temperature coefficient s_cal = s / (1 + temp_coeff * (temp - t_cal)) temp = measured temperature t_cal = reference temperature (25°C)
The calculation of total dissolved solids is the product between the temperature compensated conductivity and the tds factor corresponding to the solution that is used.
tds = k_e * s_cal k_e = tds factor tds = total dissolved solids
The following is a list of items needed in order to replicate this demo.
We recommend not opening the project directly, but rather import it into CrossCore Embedded Studios and make a local copy in your workspace.
The source code and include files of the ADuCM360_demo_cn0411 can be found here:
CrossCore Embedded Studio Application Source Code:
AduCM360_demo_cn0411 at Github
For more information on importing, debugging, or other tools related questions, please see the tools user guide.
#define DAC_OUT_DEFAULT_VAL 0.4
#define TDS_KCL 0.5
#define TDS_NACL 0.47
#define TEMP_COEFF_KCL 1.88
#define TEMP_COEFF_NACL 2.14
Following is the UART configuration.
Select COM Port Baud rate: 115200 Data: 8 bit Parity: none Stop: 1 bit Flow Control: none
|help||Display available commands|
|syscal||Perform ADC system zero-scale calibration. Before calibration, short terminals 5 & 6 in jumper P5.|
|refres||Perform Referencing to a Precision Resistance. Before referencing, short terminals 3 & 4 in jumper P5.|
|convmod(sing/cont)||set single/continuous conversion mode for ADC.|
|autoset||Autoset Gain Resistance.|
|setdac<val>||Set DAC value (Volts).|
|gainres <val>||Set Gain Resistor value (Ω). <val> = 20/200/2K/20K/200K/2M/20M|
|rtdval <val>||Set RTD value (Ω). <val> = values 100, 1000|
|pwmfreq <val>||Set PWM frequency value (Hz), <val> = values 94, 2400|
|cellconst (low/normal/high/<val>)||Set cell constant for conductivity types.|
|solution (kcl/nacl/<val_tmp_coeff,val_tds_factor>)||Set parameters for specific solution.|
|temp||Display temperature value.|
|vinput (pos/neg)||Display Positive/Negative input voltage.|
|readdac||Read DAC value (Volts).|
|rdr20s||Read Voltage on R20S (Volts).|
|rdr200s||Read Voltage on R200S (Volts).|
|readdac||Read DAC value (Volts).|
|readdac||Read DAC value (Volts).|
|rdres||Read Input Resistance (Volts).|
|cond||Display conductivity value.|
|tds||Display TDS value.|
The official tool we promote for use with the EVAL-ADICUP360 is CrossCore Embedded Studio. For more information on downloading the tools and a quick start guide on how to use the tool basics, please check out the Tools Overview page.
For more detailed instructions on importing this application/demo example into the CrossCore Embedded Studios tools, please view our How to import existing projects into your workspace section.
For more detailed instructions on importing this application/demo example into the CrossCore Embedded Studios tools, please view our How to configure the debug session section.
The ADuCM360_demo_cn0411 is a C++ project that uses ADuCM36x C/C++ Project structure.
This project contains: system initialization part - disabling watchdog, setting system clock, enabling clock for peripherals; port configuration for ADC, SPI read/write; for configuring and reading from AD7124, UART via P0.6/P0.7; UART read/write functions; for calibration and displaying the results.
In the src and include folders you will find the source and header files related to CN0411 software application. The Communication.c files contain SPI and UART specific data, meanwhile the CN0411.c files contain the calculation part, the AD7124.c files contain ADC channels handling. The default parameters are set at the run time, after initialization in the terminal window will appear information messages about the initial setup.
The RTE folder contains device and system related files:
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