A Paint Stick Guards Against Shock
Consulting engineer and RW colleague Buc Fitch wrote in about our recent discussions of "suicide installations." This is where AC above class 1 (24 volts) runs willy-nilly, unprotected and unmarked, around the plant. Buc writes that the cautions were good and very apt, considering the horror stories we've all encountered.
|Fig. 1: Something as simple as RTV or caulk can be used to guard against terminal board shocks. |
It doesn't take much in the way of effort to prevent or minimize these hazards. Buc reminds us of a tip we've mentioned previously: Cover exposed terminal strip 120 volt AC connections with caulk or Glypt insulating varnish, as pictured in Fig. 1.
Buc takes the safety a step further and includes a photo of a soft-start time delay controller he built, seen in Fig. 2. Here, you can see the most elemental of protection methods against accidental contact or shock. This controller interfaced an entire AM plant's "classic" transmitter (all 120 VAC control) to bring it online with just a single squelch relay closure. Nearly all of the terminal board connections were 120 VAC.
Yes, that is a paint stick, cut down to make a cover for the AC connections on the terminal board. Who says safety has to be expensive?
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|Fig. 2: Shock prevention doesn't have to be costly. Here, Fitch uses a piece of wooden paint stick, upper right, as a shock guard. |
In our Feb. 1 column, AM engineer Bob Meister wrote about issues he was having marrying up UPS systems to generators, especially at an AM site.
You'll recall he was able to stabilize the problem by using a Liebert GXT2 UPS. Bob reports back that his UPS systems are running fine, but this winter brought another problem: hard-drive failure due to very cold transmitter site temperatures.
Bob's AM site experienced three separate hard-drive failures due to below-freezing temperatures. The building is unheated except for the self-generated heat of the equipment. The building is also poorly insulated. Because of the failures, Bob and his team started doing research into the operating temperature range of some broadcast equipment.
The Burk ARC-16 remote control unit is spec'd to 0 degrees C. The Moseley 950 MHz digital STL is good down to –20 C, while its companion StarLink frequency-hopping spread-spectrum network unit is good down to –30 C.
The Harris DAX-1 transmitter and DEX-Star digital exciter are only rated to 0 C. The exciter runs Linux and has a hard drive in it. After the first one failed and was replaced, the new drive also failed and took the digital signal off-the-air.
Bob's research indicates that hard-drive manufacturers are inconsistent in what they spec as the acceptable lower limit temperature.
The Audemat-Aztec GoldenEagle HD monitor also runs Linux with a hard drive in it; and Bob suspects it, too, has a 0 C or 5 C low limit; it would not reboot. A personal computer running Windows went through a whole bunch of required updates, and then failed to reboot.
It's not only station engineers who want to be comfortable at the transmitter site! Bob's warning is to check the temperature if you start having transmitter site hard-drive failures, especially if there is little insulation or no building heat.
I remember one engineer's solution to an AM antenna monitor that didn't respond well to the cold. He mounted a 60 W light bulb on a panel under the monitor. Apparently, the bulb provided just enough heat to keep things happy, and provided a bonus of lighting up the interior of the equipment rack.
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|Fig. 3: A computer screen, keyboard and KVM switch all in one RU. |
Fig. 3 shows CyberResearch's Dual-Rail FoldAway monitor with 17 inch LCD and 8-Port KVM.
Since rack rooms often are short on comfortable working space for engineers, the company offers a line of FoldAway keyboard-monitors that provide separate rails for each component in a compact arrangement that occupies 1 RU when closed. Leave the monitor up to see remote PCs. Slide the keyboard out, as needed, to type commands, then slide it back in for more breathing room.
Because it comes with separate rail sets for keyboard and monitor, you can slide these elements in or out separately. When you slide both of them in, a keylock prevents unauthorized use.
Connect remote PCs via pushbuttons, AutoScan, hot keys or the OSD menu using the KVM Switch. The GFC 1708DA FoldAway configuration retails at $2,095; explore other configurations on the Web site. Info: www.cyberresearch.com.
To request a free copy of the PC Systems "Handbook for Scientists and Engineers," call (800) 341-2525 or e-mail firstname.lastname@example.org (let them know you saw them in Workbench).
John Bisset has worked as a chief engineer and contract engineer for 39 years. He was the SBE's Educator of the Year in 2006. Reach him at email@example.com. Faxed submissions can be sent to (603) 472-4944.
Submissions for this column are encouraged and qualify for SBE recertification credit.
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