Weigh Scales

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550 devices are high precision, low power, low noise voltage references featuring ±0.02% maximum initial error, excellent temperature stability, and low output noise.

This family of voltage references uses an innovative core topology to achieve high accuracy while offering industry-leading temperature stability and noise performance. The low, thermally induced output voltage hysteresis and low long-term output voltage drift of the devices also improve system accuracy over time and temperature variations.

A maximum operating current of 950 μA and a maximum low dropout voltage of 300 mV allow the devices to function very well in portable equipment.

The ADR4520/ADR4525/ADR4530/ADR4533/ADR4540/ADR4550 series of references are each provided in an 8-lead SOIC package and are available in a wide range of output voltages, all of which are specified over the extended industrial temperature range of −40°C to +125°C. The ADR4525W, available in an 8-lead SOIC package, is qualified for automotive applications.

Applications

• Precision data acquisition systems
• High-resolution data converters
• High-precision measurement devices
• Industrial instrumentation
• Medical devices
• Automotive battery monitoring

The AD7175-2 is a low noise, fast settling, multiplexed, 2-/4- channel (fully/pseudo differential) Σ-Δ analog-to-digital converter (ADC) for low bandwidth inputs. It has a maximum channel scan rate of 50 kSPS (20 µs) for fully settled data. The output data rates range from 5 SPS to 250 kSPS.

The AD7175-2 integrates key analog and digital signal conditioning blocks to allow users to configure an individual setup for each analog input channel in use. Each feature can be user selected on a per channel basis. Integrated true rail-to-rail buffers on the analog inputs and external reference inputs provide easy to drive high impedance inputs. The precision 2.5 V low drift (2 ppm/°C) band gap internal reference (with output reference buffer) adds embedded functionality to reduce external component count.

The digital filter allows simultaneous 50 Hz/60 Hz rejection at 27.27 SPS output data rate. The user can switch between different filter options according to the demands of each channel in the application. The ADC automatically switches through each selected channel. Further digital processing functions include offset and gain calibration registers, configurable on a per channel basis.

The device operates with a 5 V AVDD1, or ±2.5 V AVDD1/AVSS, and 2 V to 5 V AVDD2 and IOVDD supplies. The specified operating temperature range is −40°C to +105°C. The AD7175-2 is in a 24-lead TSSOP package.

Applications

• Process control: PLC/DCS modules
• Temperature and pressure measurement
• Medical and scientific multichannel instrumentation
• Chromatography

The circuit in Figure 1 is a precision weigh scale signal conditioning system. It uses the AD7791, a low power buffered 24-bit sigma-delta ADC along with two external ADA4528-1 zero-drift amplifiers. This solution allows for high dc gain with a single supply.

Ultralow noise, low offset voltage, and low drift amplifiers are used at the front end for amplification of the low-level signal from the load cell. The circuit yields 15.3 bit noise-free code resolution for a load cell with a full-scale output of 10 mV.

This circuit allows great flexibility in designing a custom low-level signal conditioning front end that gives the user the ability to easily optimize the overall transfer function of the combined sensor-amplifier-converter circuit. The AD7791 maintains good performance over the complete output data range, from 9.5 Hz to 120 Hz, which allows it to be used in weigh scale applications that operate at various low speeds. 

This circuit is a weigh scale system that uses the AD7780. The AD7780 is a pin programmable, low power, low drift 24-bit Σ-Δ ADC that includes a PGA and uses an internal clock. Therefore, the device simplifies the weigh scale design since most of the system building blocks are included on the chip. The device consumes only 330 μA typically and is, therefore, suitable for any low power or battery application. The AD7780 also has a power-down mode that allows the user to switch off the power to the bridge sensor and power down the AD7780 when not converting, thus increasing the battery life.

This circuit is a weigh scale system that uses the AD7781. The AD7781 is a pin programmable, low power, low drift 20-bit Σ-Δ converter that includes a PGA and uses an internal clock. Therefore, the device simplifies the weigh scale design since most of the system building blocks are included on the chip. The device consumes only 330 μA typically and is, therefore, suitable for any low power or battery application. The AD7781 also has a power-down mode that allows the user to switch off the power to the bridge sensor and power down the AD7781 when not converting, thus increasing the battery life.

This circuit is a weigh scale system that uses the AD7192. The AD7192 is an ultralow noise, low drift, 24-bit Σ-Δ converter that includes a PGA. Therefore, the device simplifies the weigh scale design because most of the system building blocks are included on chip. Since the part operates with an output data rate from 4.7 Hz to 4.8 kHz and maintains good performance over the complete output data rate range, this allows the part to be used in weigh scale systems that operate at low speeds along with higher speed weigh scale systems, such as hopper scales. 

This circuit is a weigh scale system that uses the AD7191. The AD7191 is a pin programmable, low noise, low drift, 24-bit Σ-Δ converter that includes a PGA and uses an internal clock. Therefore, the device simplifies the weigh scale design because most of the system building blocks are included on chip. The device has four output data rates and four gain settings that are selected using dedicated pins. This simplifies the interface to the ADC.

This circuit is a weigh scale system, which uses the AD7190, an ultralow noise, low drift, 24-bit Σ-Δ ADC with internal PGA. The AD7190 simplifies the weigh scale design because most of the system building blocks are included on the chip.

The AD7190 maintains good performance over the complete output data rate range, from 4.7 Hz to 4.8 kHz, which allows it to be used in weigh scale systems that operate at low speeds along with higher speed weigh scale systems, such as hopper scales.

This circuit is an ac excited weigh scale system that uses the AD7195, an ultralow noise, low drift, 24-bit Σ-Δ ADC with internal PGA and drivers to implement ac excitation of the load cell.

The AD7195 simplifies the weigh scale design in low offset systems because most of the system building blocks are included on the chip. The AD7195 maintains good performance over the complete output data rate range, from 4.7 Hz to 4.8 kHz, which allows it to be used in weigh scale systems that operate at low speeds along with higher speed weigh scale systems.

UG-1201 describes the evaluation board for the ADA4625-1 low noise, fast settling, single supply, rail-to-rail output (RRO), junction field effect transistor (JFET) op amp in an 8-lead small outline integrated circuit (SOIC) package with an exposed pad. The design of this evaluation board emphasizes simplicity and ease of use. This evaluation board is a 2-layer board that accommodates edge mounted SubMiniature version A (SMA) connectors on the inputs and outputs. The SMA connectors allow efficient connection to test equipment or other circuitry.

The evaluation board ground plane, components placement, and power supply bypassing are optimized for maximum circuit flexibility and performance. The exposed pad of the ADA4625-1 is connected to the ground plane on the evaluation board to enhance thermal and noise performance. The evaluation board uses a combination of surface mount technology (SMT) component case sizes 0603 and 0805, with the exception of the bypass capacitors, Capacitor C3 and Capacitor C5, which have a maximum standard size of 1206. The evaluation board also features a variety of unpopulated resistor and capacitor pads, which provide the user with multiple choices and extensive flexibility for different application circuits and configurations, such as active loop filters, transimpedance amplifiers (TIAs), and charge amplifiers.

The ADA4625-1 data sheet covers the specifications and details of the device operation and application circuit configurations and guidance. Consult the data sheet in conjunction with UG-1201 for a better understanding of the device operation, especially when powering up the evaluation board for the first time.