电子秤被广范应用于重量测量行业中。从质量超轻的试剂到大型集装箱,称重都为从化学反应到商品管理的各种过程提供关键信息。所有现代化电子秤的关键元件都是模/数转换器。MAXREFDES75#将完整24位ADC集成至高性能系统,执行小信号(低至±25mV满幅)24位测量,同时产生高压传感器电源,从而生成与输入信号成比例的0至10V输出。
MAXREFDES75#参考设计的特性包括:
MAX11270
MAX542
电子秤被广范应用于重量测量行业中。从质量超轻的试剂到大型集装箱,称重都为从化学反应到商品管理的各种过程提供关键信息。所有现代化电子秤的关键元件都是模/数转换器。MAXREFDES75#将完整24位ADC集成至高性能系统,执行小信号(低至±25mV满幅)24位测量,同时产生高压传感器电源,从而生成与输入信号成比例的0至10V输出。
MAXREFDES75#参考设计的特性包括:
MAX11270
MAX542
Figure 1 shows the block diagram of the MAXREFDES75#.
Figure 1. The MAXREFDES75# reference design block diagram.
The signal chain begins with the sensor signal feeding directly into the MAX11270. No external op amp is necessary because the PGA is integrated in the MAX11270. Following isolation via the MAX14850, the MAXQ622 reads the input signal, applies zero-offset and weight-factor, and presents the resulting weight. The MAXQ622 calculates a DAC value, based on DAC calibration and output range mapping and writes this to the DAC. A variety of sensor power options are available, outlined in Table 1.
Table 1. Sensor Supply Configuration
ADC Input Configuration | Connectors | Shunt Positions |
---|---|---|
10V generated on MAXREFDES75# | Output: S+ Bridge Output: S- Bridge Ratiometric setup Ratiometric setup |
JP5: horizontal JP6: horizontal JP2: 2-3 JP3: 2-3 |
3.3V generated on MAXREFDES75# | Output: S+ Bridge Output: S- Bridge Ratiometric setup Ratiometric setup |
JP5: vertical JP6: vertical JP2: 2-3 JP3: 2-3 |
Sensor supplied externally ratiometric measurement | Input: S+ Bridge Input: S- Bridge Ratiometric setup Ratiometric setup |
JP5: open JP6: open JP2: 2-3 JP3: 2-3 |
Sensor supplied externally use voltage reference | Input: S+ Bridge Input: S- Bridge Ratiometric setup Ratiometric setup |
JP5: open JP6: open JP2: 1-2 JP3: 1-2 |
The MAXREFDES75# is equipped with multiple sensor-supply options. Either 10V or 3.3V may be used to excite the load cell. Excitation at 10V will provide the highest performance, however, it will require additional components, and hence increase cost, in any final design. The 3.3V rail is required for ADC operation so it will be available in all configurations. Furthermore, the ADC may be configured to operate in a ratiometric mode, with the reference-derived resistor-divider from the 10V rail, or from the MAX6126 voltage reference. The ratiometric method is generally preferred, however, the voltage reference provides the user flexibility to evaluate the system without the changes in gain contributed by the system.
The MAXREFDES75# board receives power from a single DC source of 9V to 40V, 200mA through the X2 terminal block. The MAX17501 generates an +8V rail from the variable input supply. The MAX16910 LDO generates 3.3V for the MAXQ622 from the 8V rail. The MAX13256 generates isolated positive and isolated negative rails for the ADC, DAC, voltage reference, load cell, and analog output. The MAX16910 LDO generates VDD for the MAX542. The MAX8510 LDOs generate AVDD and DVDD for the MAX11270. The MAX9633 generates a low-noise 10V supply for the load cell.
Required equipment:
The MAXREFDES75# board is fully assembled and tested. Follow the steps below to verify board operation:
Positive supply for load cell S+, negative supply for load cell S-.
Load cell output connects to IN+ and IN-.
Note: Remove all weights from the load cell prior to power-up, avoid vibrations while the first 10 measurements are taken.
The recommended process is to use the “Automatic Calibration” tab, which leads the user through the entire process. The calibration factors established by the automatic calibration are populated in the appropriate text boxes in the “Manual Calibration” tab and can be reviewed after calibration.
Connect a precision multimeter between AOUT and AGND on the right side (if oriented such that the display can be read) of the board. Click the “Calibrate DAC” button.
Click “Calibrate Output”.
A pop-up window asks the user to enter a weight in grams that should produce 0V output.
Note: Weights below that will also produce 0V.
And enter the weight that should produce 10V output.
Note: Weights above that will also produce 10V.
Click the “OK” button.
Stand-alone operation (after the first calibration was done)
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Required equipment:
Hardware Files
Schematic
Bill of materials (BOM)
PCB layout
PCB Gerber
Software Files
Calibration GUI
Firmware Files
MAXQ622 Platform