DHT24

The DHT24-02 is a fully digital servo amplifier designed for long life in harsh environments (operates from -10°C to 175°C) for down-hole applications such as Directional Drilling, Horizontal Drilling, MWD, LWD, and Wireline. The amplifier can control a BLDC servo motor in torque or velocity loop mode and can be digitally configured for a wide range of motors.

Power to drive the motor is provided from the filtered Tool Power supply line (24 VDC) and a 3.3 V digital supply for the control circuitry. Built into the drive is a Power Saver mode that reduces the current draw when the motor is disabled, thereby increasing the battery life.

The amplifier contains a high performance DSP to perform all control functions, including the creation of PWM signals used to drive the power MOSFETs. The DSP communicates between the amplifier (as the slave) and the user’s main processor board (as the master) via an SPI port. For applications needing more than the standard command set, custom commands can be created per the OEM’s requirements.

In addition to the SPI port, an asynchronous UART port (SCI) is provided for debug and serially programming the DSP Flash memory. These signals are 3.3 V logic levels, and need to be externally converted to RS-232 in order to connect them to the serial port of a computer or terminal. This SCI port operates at 9600 baud, N, 8, 1.

The amplifier is a circuit board without base or housing. The board is 7” x 1.22” x 0.093”, polyimide 85N material ready to be integrated into a tool. The OEM will typically stake, dam, and pot the assembled PCB to provide additional protection against shock and vibration.

Additional benefits of sensorless control include reduced system cost and size. The motor cost is reduced because of the removal of the feedback device and the further reduction of material and labor associated with the wiring of the feedback device. The reduction of wiring also reduces the space required to install the drive system.

A sensorless drive is well suited for applications that do not require position control, do not have varying load, and do not require operation near zero speed. Therefore, a sensorless drive is ideally suited for pump applications.

For a Best-of-Both-Worlds solution, the drive has an option with Halls feedback and an algorithm that automatically switches to Sensorless control if the Halls fail. This enables the user to continue operating the tool and replace the motor during the next pull-out.

Features & Benefits

High Temperature Operation – independently tested to operate at higher than 175°C
Flexibility – The drive can operate from Halls and automatically switch to Sensorless if Halls fail
Sensorless Control – Option to eliminate the Hall sensors and associated cable without sacrificing the advantages of the advanced commutation or losing staring torque
Programmable Starting Current – The OEM can program the ramp rate and current limit for the starting routine
Ruggedization – The printed circuit board and components are designed and situated to survive the shock and vibration associated with down-hole services, such as MWD and LWD, and are ready to be potted into an OEM tool
Small Size - 7” x 1.22” for the base model
Power Saver Mode – activated extends the life of the battery
Programmable Start-up Current Control – Parameters enable the OEM to set a current limit and ramp rate for the start-up routine
Advanced Commutation –Space Vector Commutation and Flux Vector Current Control improves bus voltage utilization for improved torque/speed curves, improved energy efficiency, reduced heat dissipation, and provides smoother operation compared with standard sinusoidal or trapezoidal commutation
Digital Tuning – Optimizes performance, enables cloning, eliminates pot drift, and can reduce inventory
Control Loop – For pump applications, the drive can receive an analog signal from a pressure transducer and can be programmed to vary the speed in proportion to the signal
Extensive Fault Protection – designed to protect the components, the amplifier, and the motor, but can be individually disabled by the OEM
Customization - PCI can modify the drive to make it compatible with an OEM’s system

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