Tech Talk: Timing relays are confusing to me. Can you explain the difference between single-shot and interval timers? What happens if the output driving the relay changes state during a timing sequence?

When all of the possible combinations of timing states and initiating device transitions are considered, a stronger word than “confusing” may be in order! Below are some timing diagrams and sequences of operation in simple terms that may be of help. Since it is an electronic circuit that is energized rather than a coil, the […]

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Tech Talk: 3-Phase Motor with One Lost Phase

Q: What happens to a 3-phase motor when one of the phases is lost? The most extreme case of phase unbalance is the total loss of one of the three phases and is known as phase loss or single phasing. Phase loss can be caused by a broken power line, a lightning strike, an open […]

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Relay Fundamentals

Open an HVAC control panel, and you’re likely to find at least one relay mounted inside. Sometimes you find lots of relays! Even though relay technology has been around since the 1800s, there is still a need for relays in control panels. What components make up a relay? How are relays typically shown in wiring […]

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Using a Multimeter Series – Resistance Measuring Basics

“Resistance is futile, Buwhahaha” exclaimed the villain, rubbing his hands together in glee as our hero struggled to free himself from the ropes that bound him. Yep, we’ve all seen those Grade B movies.  Maybe in that situation resistance is futile, but in the world of electronics and HVAC controls resistance (electrical resistance) is very […]

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Using a Multimeter Series – Voltmeter Basics

If you live in the world of HVAC design/installation, sooner or later you’re going to need to take measurements on a circuit using a voltmeter (even if it’s “not your job,” we all know how that goes). So we thought it would be a good idea to put together some basic instructions on using a […]

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“Currently” Playing: Connecting A 4-20 mA Constant-Current Signal To Multiple Loads

One of the most popular and long-lived methods for transmitting analog control signals in the HVAC and industrial control worlds is the “constant-current signal loop.” In this scheme, the value of the current flowing in the circuit is the control variable, rather than any voltages that may appear at different points in the circuit. The […]

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Networking 101: BAS Network Cabling

The various devices comprising a building automation network are either connected by cables or talk wirelessly to each other, or possibly a combination of both.  In Networking 101, we are going to concentrate on network devices connected by cables.  Let’s take a look at the different types of network cables typically encountered in building automation […]

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Q: The intrinsic safety spec I’m reading calls for an isolated ground. Isolated from what?

Answer: A true isolated ground is not connected to any ground that can ever carry fault current from unrelated parts of the electrical system. It is best to run it directly to grounded building structural steel, an underground metal water pipe, or a separate grounding electrode from the building electrical service as described in Article […]

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Temperature Sensor Curve ID Numbers

  Need help figuring out what type sensor you need for your automation system?  This handy temperature curve chart might help.  If not, give Kele a call!   Sensor Type Temperature Sensor Description  Typical Sensor User 3 10,000Ω @ 77°F, Type III material    AET, American Automatrix, Andover, Carrier, Delta, Invensys, Teletrol, York 21 2252Ω @ […]

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