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Phone:
800-324-8388 970-249-6129 Fax: 970-249-8919 |
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Phone:
800-324-8388 970-249-6129 Fax: 970-249-8919 |
TONE TELEMETRY COMMUNICATIONS
Telemetry and Control
Telemetry is the art of transmitting measurements of physical phenomena over a distance. The basic restraints are the response time needed and the noise in the media of transmission. The transmission media may be wire lines, telephone networks, radio, microwave, light, water, etc. Da-Tel manufactures frequency division and time division telemetering systems using telephone lines, microwaves and radio as transmission media. The art is obtaining the most channels of data in the allowed bandwidth with good response time, reliability, and noise immunity at lowest cost and longest life. Da-Tel selects technology for each project as to gain customer acceptance. The technologies are:
1. Frequency Division, Frequency Shift modulation See Standard Channel Frequencies
2. Modem and Time Division, voice band
3. The application and use of a telemetering system dictates the technology recommended by Da-Tel Research Company.
Dedicated Two Wire Lines / Dial-Up Lines
The traditional communication links for Da-Tel telemetry equipment are dedicated two or four wire leased telephone lines and dial-up lines. Dedicated two wire telephone lines should exhibit a 3dB frequency response curve from 300 to 15,000 Hz when loaded and driven by 600 ohm impedance loads. No resonance points should occur in the response curve due to open lengths of wire left connected to the line. The attenuation is approximately 1dB per mile for #22 AWG copper wire. Cross talk from the cables of the telephone company should be less than -55dB, two way repeaters are required for distances greater than 20 miles when tones are in the voice band.
The Public Dial-up Telephone system can be used for telemetering and data-telecommunications provided the tones are within the 300 to 3000 Hz voice band and the composite signal level is held below -7 dBm.
All Da-Tel data and metering equipment can be used on dial-up lines or fiber optic lines on a time-sharing basis. Many applications require monitoring and control for a short time each day. Da-Tel modems can be used to down load computers at required intervals or delivering RS-232 data. Wireless Communications
Radio frequency transmitter and receiver connections are available depending upon application for FCC licensing requirements or available frequency and low power no license requirement situations. Da-Tel equipment could also use frequency shift or spread spectrum modulation for voice bands of 300 to 3000 Hz. See Application Diagram
All Da-Tel standard tone modules use linear LC filter networks to divide the frequency bandwidth allowed into small bandwidth channels adequate to meet response or update times. Linear LC filters withstand the greatest composite peaks, imbalance of signal levels, noise peaks and out-of-band extraneous signals from crossed telephone lines and voice channels.
In time division technology the allowed bandwidth is efficiently used by modems to attain the highest digital bit rate that the modem allows to go over the line with the noise on it. A short code or message is used with parity and double scan error detection. For large systems and SCADA, FSK tone channels or separate lines are used to back up basic data, as one failed component can shut off all channels of a time division telemetering system.
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