![]() ![]() The HART modem modulates and demodulates the signal using FSK, just like the Bell 202 system. The primary measured value could be the temperature or pressure level measured in the field. Similarly, in industrial applications, the signal that must be monitored at all times is known as the primary measured value. In the caller ID example, the voice signal represents the PV. Once the handset was lifted the FSK signal would terminate and the modulated signal carrying the voice information would then be demodulated and transmitted to the receiver ear-piece. The inclusion of the Bell 202 FSK allowed the transceiver to send large amounts of data before the receiver handset was lifted and was then filtered and used to communicate caller ID information. The caller ID information does not interfere with the voice signal so that all of the information can transfer over the same physical wiring. The data transfers at a rate of 1,200 bps using 1,200 Hz and 2,200 Hz frequencies representing a binary 1 or 0, respectively, as shown in Figure 1.įigure 1: Frequency-shift keying modulation Audio frequency-shift keying (FSK), which uses modulated tones to produce a digital signal, transfers the digital information containing the phone number. In the late 1990s, the telecom industry adopted the Bell 202 standard to transmit caller ID information on the same line as voice signals. But first, let’s look at how the method originated. In this post, I’ll look at what HART is and how it works. The HART protocol has been a common method for communication in industrial automation for many years. One downfall of this method is that you can only monitor one variable at a time, so the Highway Addressable Remote Transducer (HART) protocol enables the transfer of more information on the same two-wire system. The primary variable (PV) is communicated as a current level between 4 mA and 20 mA on a two-wire loop-powered system. One way to monitor field equipment automatically is through 4-20 mA loop sensor transmitters. It would be unrealistic for an engineer to monitor every piece of equipment in the factory (and that certainly would decrease productivity). The blog post was co-authored by Audrey Dearien.Ĭommunications in industrial automation systems enable the transfer of data, commands and other information to streamline process control and factory automation. ![]()
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