It is my belief that the traditional broadcast view of remote control and telemetry of a broadcast transmitter site provides the engineer with an incomplete picture of the state of the building environment and the systems within. I'm certain you have on more than one occasion received a call from your remote control unit due to an alarm condition and after interrogating the system and clearing the alarm were left with some doubt as to what is going on at the site. Of course, the only way to answer that little nagging voice is to get in the car and head for the tower. But if we engineer our facility correctly, and funds are made available and carefully spent, we can perhaps make that inspection trip at more suitable times than dinner or the middle of a movie.
When I set out to design a complete remote control system, I try my best to apply what I call the NASA model. When NASA launches a multimillion-dollar spacecraft to Pluto, that spacecraft is not returning. If a technical issue develops, NASA or JPL cannot send a repair tech to swap a board, reset a breaker or an over-voltage alarm. Further, anything that can be measured within that spacecraft is included in the design so the engineers here on the third rock can work the problem with a more or less complete understanding of the status of the equipment. In this manner, engineers may perform workarounds and bypasses to keep the spacecraft running and preserve the value of the mission. I view our precious transmitter sites in much the same way. Some of our sites are so remote or so challenging to access that they might as well be on a trajectory to Pluto.
I have seen time and time again that a given transmitter site was wired with the barest minimum of status, metering and control. Often I see little if any status brought out, no means of monitoring critical environmental parameters, no means of monitoring line voltage, generator condition, or transmission line pressure, nor whether or not the nitrogen tank is full or nearly empty. Many engineers connect a room or stack temperature sensor, but nothing with regard to the state of the HVAC units, smoke detectors or building intrusion. A very good share of the devices on the market provide dry closures or analog outputs that will provide insight into their current operation. Being technical geeks, we are able to devise our own means of monitoring equipment status using readily available parts from component vendors. The work up front will pay long-term dividends.
A key element
One of the key elements of remote site management is transmission line pressurization systems monitoring. One of my personal favorite vendors is Omega Engineering. This company is a peerless engineering toy store with products for measuring pressure, flow, temperature, humidity, levels, stress and strain, PH, etc. This company caters to industrial environments.
Performance at a glance
Multitrack DAW with full effects
Supports up to 48kHz sample rate
Supports Direct-X and VST plug-ins
Reads/writes multiple audio file formats
In the final analysis, our transmitter sites or remote studios are much the same in the sense of the need for access, reliable telemetry and control. I can easily visualize the broadcast application of many of their products, such as monitoring transmission line pressure, remaining pressure in the nitrogen tank, monitoring the temperature of key components in an antenna combiner system (transmission line sections, filters, couplers, etc.), three-phase voltage and current monitoring, and precise industrial-grade control of many of our critical systems.
One intriguing application includes employing one of Omega's electrically controlled proportional control valves to remotely adjust transmission line pressure, and monitor the result with the devices I'll look at further in this article. One point: inasmuch as the devices sold by Omega are of industrial-grade, they are by design, manufactured to operate reliably in areas of high EMI such as that found in our transmitter facilities. You will see by perusing the catalog that most of its devices are designed to work with the industrial 20ma standard, and being of a current loop design, resiliency to EMI is inherent.
Various connectors are available on the transducers, including a twist-lock, cable connection and a mini-DIN.
There have been a few pressure-transducer units manufactured for broadcasters to monitor transmission line pressure. In my view, these units were/are of poor quality and may be easily damaged in the installation process. They leaked in some cases out of the box, which defeats the whole purpose. Omega makes a complete line of high-grade precision pressure transducers to permit remote telemetry of gases with various options. These options include transducers with milli-volt outputs, 0-5Vdc outputs, 0-10Vdc outputs, 20ma current loop interface, and the choice of absolute pressure or gauge pressure with various ranges of pressure. Other options include the type of signal interface connector: mini DIN, pigtail or twist-lock.
I chose two models for use with our remote control system: the PX219-015G5V transducer for 0 to 15psi, gauge pressure, 5Vdc output with a ¼" NPT connector for monitoring transmission line pressure; and the PX319-3KG5V transducer for 0 to 3,000 psi, 5Vdc output, and gage pressure with ¼" NPT fitting to monitor our nitrogen tanks. With the application of these two devices, I now have a complete picture of the condition of my pressurization systems and can set alarms with my remote control for low line pressure and low tank pressure (the latter lets me know if it's time to call the nitrogen guy). Thus far, these transducers have been performing flawlessly. In keeping with the NASA model, I now feel I'm a step closer to having that complete picture of the conditions at my sites.
Incidentally, I should mention Omega also sells a product that can be used to monitor pressure and temperature with a built-in Web interface and logging capability, the IPTX-D. I will be testing this device soon.
Sloatman is the chief engineer for the Cox stations in Orlando, FL.
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