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REMOTING SIX SENSORS ON ONE TWISTED PAIR - PART 1

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REMOTING SIX SENSORS ON ONE TWISTED PAIR - PART 1

Postby Glovisol » Mon Feb 08, 2016 7:55 pm

Master capture 1.jpg
RS485 in operation: note correspondence between mV readings even without calibration
1. OVERALL DESCRIPTION & GENERAL CONSIDERATIONS - REMOTING SOLUTION B3


Coupling the microprocessor’s capabilities of Arduino to the DrDAQ or 1012 Pico Data Loggers can extend Picolog’s applications in many different directions and solve difficult technical problems. In the writer’s experience Data Acquisition in industrial sites is in general far from easy. If the sensor and the Data Logger have to be placed far from the PC, USB interconnection cannot be used, because USB is limited to a few metres of cable. Furthermore many environments are not suitable for local DrDAQ installation, because of physical/environmental conditions, as well as noise/ground loop problems. Analogue transmission solutions can be very reliable (see the Amplitude Modulation post) but are limited to one channel per two conductor twisted pair available: as soon as multiplexing is employed, a multiple conductor is required for switching and external noise again poses problems.

A small and low cost RS485 transceiver using twisted pair conductor, based on the Arduino 1 Micro and working on distances of over 1,000 metres, (3,000 ft) has the potential of remoting up to six sensors, with 8 Bit capability and a standard dynamic range of 0 to 2.5V, perfectly matching the DrDAQ specification.

The presently proposed system works at low speed (PWM 500 Hz), but, by software modification, there is potential for two channels at high speed (PWM @ 4KHz) and four at medium speed (PWM @ 1 KHz). The PWM signals only appear at the output of the Master, because the twisted pair interconnection between microprocessors works with the high noise rejection, long distance RS 485 Standard at up to 57,600 Baud Data Rate.

Generally speaking, complex Arduino projects are not easy for the inexperienced, because even if it is true that suitable technical information is generally available, the problem is that this information is parcelled in bits and pieces in very many different sites all over the Internet. Software examples are also available, but with little or no explanations, often incomplete and ridden with errors. The approach in the present work is that of fully explaining every side of the project with care and of providing all necessary information, so that even a beginner working with Arduino and with a basic understanding of electronics will be able to get to the planned result.

This project is organized as follows:

• Description of System Operation.
• Planning strategy for Arduino Micro implementation.
• Arduino Demo software. This is a simplified example carrying only one channel with full and detailed explanation of theory of operation. Those interested can quickly get an idea of system performance.
• Modem connections; RS485 Standard and twisted pair/coaxial pair media with data & simulations.
• Arduino 6 channel software and System performance data.
Glovisol
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