Saturday, May 7, 2011

【 Weak current College 】 various common transmitter features at a glance 】

Sensor and transmitter in equipment, instrumentation and industrial automation area play a decisive role. And sensors, transmitters, in addition to the non-power into measurable power, also has a Zoom effect. This article briefly describes the various types of transducer characteristics for consumer choice.
First, the integral temperature transmitter
Integral temperature transmitter temperature probe by (thermocouple or resistance thermometer sensor) and two wire solid electronic modules. Adopted in the form of solid modules directly installed in temperature probe connection box, thus forming integrated transmitter. Integral temperature transmitter is generally divided into two, Thermocouple type type.
RTD temperature transmitter is a base unit, R/V conversion unit, linear circuits, and reverse, current limiting protection, V/I conversion unit, etc. Temperature resistance signal conversion is enlarged by linear circuit resistance to temperature and compensation of nonlinear relations, V/I converter circuit output one and after being measured temperature into a linear relationship between 4 ~ 20mA signal of constant current.
Thermocouple temperature transmitter general reference source, cold-junction compensation, amplification unit, linearization, V/I convert, fault-handling, and reverse, current limiting protection circuit modules. It is produced by the thermocouple thermoelectric power amplification by cold-junction compensation, then CAP by linear circuits eliminate thermoelectric power and temperature of nonlinearity, convert the last zoom 4 ~ 20mA current output signal. In order to prevent the thermocouple measurement due to galvanic broken wires but allowing temperature failure caused the accident, the transmitter also has a power-off protection circuit. When the thermocouple wire breaking bad or solutions, the transmitter will be output maximum (28mA) to enable the instrument to cut off power supply.
Integral temperature transmitter with simple structure, saving the leader, the output signal is big, strong anti-interference ability, linear, and display instruments simple, solid modules have seismic-proof, reverse and current limiting protection, reliable, etc.
Integral temperature transmitter output is the unified 4 ~ 20mA signal; and computer systems, or other general instrument match. You can also request made explosion or fire-type measuring instrument.
Second, the pressure transmitter
Pressure transmitter also known as differential transducer, mainly by the load cell sensor, modules, circuit, display table headers, watch and process connections, etc. It can be received by gas, liquid pressure signal into standard current supply voltage signal to indicate alarm, recorder, controller and other secondary instrument for measurement, instructions and procedures.
The measuring principle is: the process pressure and reference pressure acting on integration respectively Silicon pressure sensitive element ends, its differential pressure that silicon chip deformation (shift is very small, only μm), so that the Silicon semiconductor technology made of full-motion Wheatstone bridge in external current source output proportional to driven by the pressure of the mV-voltage signal. Because of the strong resistance of silicon materials, so the output signal of linearity and variation index are very high. Work, the pressure transmitter would be converted into physical measuring mV voltage signal level, and conveyed to the magnification is very high and you can cancel each other out temperature drift of differential amplifier. Enlarged signal voltage and current is converted into the appropriate current signal, through non-linear calibration, last generation and input pressure into the standard linear correspondence between current and voltage signals.
Pressure transmitter under pressure range can be divided into general pressure transmitter (0.001MPa ~ 20MP3) and micro-differential pressure transmitter (0 ~ 30kPa).

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