It is often necessary to inspect a region inside a confined area. In medicine, an endoscope is used to look inside the body to examine organs. Endoscopes can examine gastro-intestinal, respiratory and urinary tracts as well as internal organs through a small incision. An endoscope captures images through its long tube, which can be rigid or flexible. Additional instruments for cutting, grasping and other functions are often attached to the endoscope to permit minimally invasive procedures that improve patient care and minimize recovery time. When used in a technical application to inspect confined spaces, it is often referred to as a borescope. Borescopes are used to inspect machinery interiors, building walls and to search for victims in collapsed buildings.
Endoscopes, or borescopes, have three basic requirements in common:
A light source and tube are used to guide the light to the subject A light source to illuminate the subject
A lens or fiber optic system to capture light reflected from the subject
An image-capture system to capture, process and store or display the image
TI’s broad product portfolio supports the entire image chain: generating light, capturing an image, signal conditioning and image processing.
LED drivers supply a bright light source with excellent directionality and minimal waste heat. These drivers are versatile and permit selection of LEDs optimized for an application’s spectral requirements. The resolution of current steps impacts the precision of the illumination control; 14-bit LED controllers allow for precise control of illumination levels and illumination timing.
The image sensor detects the reflected light and converts the light to an analog electrical signal. Depending on the image sensor’s location, low-noise line drivers may be needed to transmit the signal over the light tube’s length. Critical considerations for line drivers are low power, noise immunity and data rate. LVDS technology provides up to 800Mbps with voltage swings of a few tenths of a volt and high rejection of common-mode noise.
Essential to the final image quality is the Analog Front-End, AFE. The AFE conditions the sensor’s analog electrical signal and converts image information to a digitized representation. Critical to AFE selection is the ability to condition the signal to correct sensor-induced distortions such as: dark current cancellation; reset level variations; defective pixel correction; and DC off-set variations. Depending on the signal level, the presence of Programmable Gain Amplifiers (PGAs), the linearity of the PGAs and the range of gains available may also be important. During digitization, the number of bits will determine the contrast of the image. Typically, one wants to digitize the initial data with two to four bits more precision than is desired in the final image. Thus, if 8-bits of final image data are required, then initially digitize to 10-bits to allow for rounding errors during image processing. Finally, when color reproduction is critical, then the Differential and Integral Non-Linearity (DNL, INL) should be minimized.
Endoscope: A lighted optical instrument used to get a deep look inside the body and examine organs such as the throat or esophagus. An endoscope can be rigid or flexible.
Specialized endoscopes are named depending where they are intended to look. Examples include: cystoscope (bladder), nephroscope (kidney), bronchoscope (bronchi), laryngoscope (larynx + the voice box), otoscope (ear), arthroscope (joint), laparoscope (abdomen), and gastrointestinal endoscopes.
2.7. Field transmitter: Temperature sensor (Полевой преобразователь: Датчик температуры)
F ield Transmitter: Temperature sensor Solutions from Texas Instruments
Temperature sensors are used to measure temperature and have a wide range of uses in industrial, commercial applications. Temperature measurements are made using RTD (Resistance Temperature Devices), Thermistor or Thermocouple.
RTD and Thermistor utilize the property of Change in Resistance according to temperature to measure voltage drop across the element and calculate the temperature. A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference, known as Seebeck effect. Ambient temperature is added to this calculated temperature difference to measure actual temperature. The process of measurement of Ambient Temperature is known as cold junction compensation.
Temperature transmitters are of two types. The conventional Field Transmitters working as a part of Industrial control loop that are line or loop powered and the Wireless or Handheld temperature sensors that are battery powered.
Excitation Technique: RTDs and Thermistors being passive elements need a current excitation source to make measurements. Highly stable and accurately matched current sources with low drift are critical to making 3 wire RTD measurements. TI’s temperature sensor front-ends have high precision on-chip current sources. Accurate measurement of the ambient temperature for Cold Junction compensation in Thermocouple measurements can be made using the high accuracy on chip temperature sensor. Thus the TI analog front-end for temperature measurement is a single chip solution that provides all aspects of signal conditioning needed for RTD, Thermistor and Thermocouple measurements.
Signal Conditioning/Signal Acquisition and Processing: The output range of the temperature sensor is very small and thus the signal needs to be amplified before processing to prevent introduction of errors. The signal chain has to handle the small signal accurately in presence of noise. TI’s temperature sensor front-ends have an input multiplexer, high impedance PGA and high resolution sigma-delta modulator all integrated into a single chip. The low noise, chopper stabilized PGA provides the versatility of scaling the gain as needed in accordance with how small or large the output from the sensor is. High end products also have integrated features for system diagnostics and fault monitoring. A further level of system calibration could be implemented in the MCU.
Interface and Communication: Traditional analog (4 - 20mA) interface remains the popular choice for industrial control and sensor applications. The other popular protocols include HART, Profibus and IO-Link. TI's IO-Link interface products have integrated regulators and diagnostic outputs. In addition, wireless options based on IEEE 802.15.4 protocols are becoming more prevalent. TI is committed to provide solutions for both traditional and emerging industrial interfaces.
Power Management: The Field Transmitter can be powered in one of three ways. Line powered transmitters are commonly powered by voltage rails of 12V, or 24V. Loop powered transmitters are powered by the 4-20 mA loop. Such transmitters require extremely low power architectures as the entire solution has to be powered off the loop. TI provides high efficiency Step Down converters with low quiescent current and low output ripple appropriate for Line and Loop powered transmitters. Battery powered transmitters powered can be designed using TI's low power Buck and Buck-Boost converters. The DC/DC buck converters offer over 95% efficiency over a wide battery voltage range, even with input voltage down to 1.8 volts extending battery life. Special Buck-Boost converters generate a stable required output voltage and supply constant current for over- and under-input voltage conditions and support various battery configurations.