What's the Difference Between DC Voltage and RMS Voltage?
-- RMS stands for Root-Mean-Square. It's a mathematical formula for the continually changing voltage -AC, or unsteady DC-. It shows as an RMS Voltage, not just the instantaneous voltage, but over short sample time, it shows how much equivalent DC Voltage is required...Read More
What is the Difference Between Thermostat and Fire Alarm System Cables?
-- The insulation on the Low Voltage Thermostat cables is usually rated by the manufacturer to be 30 volts, while the insulation on Fire Alarm System cables is rated by the manufacturers to be 300 volts. The rating voltage is for all voltages: for continuous DC voltages, like the voltage that comes from a battery, and for short term transient voltages, like the peaks of voltage on AC signals or power...Read More
What Value Should be Used for a Flyback Diode?
-- A motor coil, relay coil, fire alarm door holder, etc. operates by magnetism. Moving electrons in a wire creates magnetism. There is a direct relationship between electrons moving in a wire or a coil and the magnetic field around the wire. If the electrons are...Read More
What is the Extra #6 AWG Wire Jumper For?
-- One of the reasons the neutral wire is connected to ground is to provide a first-ground before there is a second, powered ground fault. If there is a powered ground fault, rather than someone being electrocuted, the fuse will be blown...Read More
Is Water a Non-Linear Resistor?
-- The actual resistance of water is affected by the impurities in the water, how much water there is and how far the electricity has to go through the water, water temperature, and by the voltage that is applied...Read More
Is Safety-Ground the Same as Signal-Ground?
-- Small voltages present on a building's safety-ground usually isn't a problem. However, when those small voltages present on ground are compared to the small voltages often used for signal transmission, the voltages on ground are often huge...Read More
How is this Full Wave Bridge Rectifier Used?
-- This is a special application, so it's used as a half-wave rectifier. For theoretical purposes, D4 and D3, being in parallel, are a single diode. The package of diodes may say -Full Wave Bridge Rectifier-, but the package is being used as -Half Wave Rectifier-...Read More
Does EMI/RF Filtering Work with Fire Alarms?
-- EMI/RF stands for Electro-Magnetic Interference / Radio Frequency. It's a generic term for -Interference caused by electrostatic, magnetic, or both signals in the radio spectrum of signals.- Depending on who you ask about what is included in the radio spectrum of signals, the low frequency end of the spectrum could be considered as low as 50 kHz, and the high end of the spectrum could be considered to reach the near infrared frequencies...Read More
Why is the Termination Resistor Equal to the Characteristic Impedance?
-- The CAN system is a single signal path, it is without t-taps as such, and it has a termination resistor at each end of the path. There can be dozens of modules attached along the CAN signal pathway. Each module can be used to transmit data into the CAN pathway, and each module monitors the data on the pathway...Read More
What Causes the Noise in the Sound System?
-- To test if it is the source of the noise, you have to disconnect both wires for the relay from the fire alarm panel so the fire alarm system isn't injecting any signal into the microphone cables. Make sure there is no power from the fire alarm control panel going through the fire alarm wire inside the conduit...Read More
What is an Arc Flash?
-- Burning, blinded, deafened, an electrician is thrown across the room; having reached into a live electrical panel, all he did was to drop... Read More
What is Capacitive Lag?
-- A capacitor is defined as -Two Conductors Separated by an Insulator-. Wire is a capacitor. Wire also has resistance, and the power supply -digital transmitter or signal generator- sending a signal through the wire has resistance...Read More
Does Low Voltage mean Power Limited?
-- Many times, and from many people in all levels of the power limited community, and not just the fire alarm community), I have heard the words -low voltage- used to mean -power limited-. I know this is...Read More
Why was the Automatic Voltage Regulator Damaged?
-- The Automatic Voltage Regulator is an electronic device. As such, it is itself capable of being damaged from transient voltage spikes that come in on the power line. Yes, it is designed to reduce voltage spikes that come in on the power line, but the voltage spikes that it's designed to correct are relatively long. Lightning strikes or work on the outside power lines can induce voltage spikes that are far shorter...Read More
What is a Flyback Diode?
-- Someone Thinks the Flyback Diode is Important. Manufacturers all over the world spend good money installing these diodes, they must think they're ... Read More
Is Conduit Ground Good Enough for Electronics?
-- The National Electrical Code (NEC) is concerned with fire safety and with electrical safety. The electronic technician is concerned with those issues, but the electronic technician is also concerned with signal transmission ...Read More
Shouldn't the Ground Rods be the Same Resistance?
-- The grounding-rods themselves are large electrical conductors. The resistance of each rod, from one end to the other is essentially zero ohms. For all practical purposes, your ohmmeter will say zero ohms for each rod. They are connected using a large diameter braided copper cable, which your meter will also show as zero ohms...Read More
How Does a Relay Work?
-- They're electrical switches; like a light switch on the wall, a relay turns on or off the electricity. The difference between a light switch on the...Read More
How Do I Use a Multimeter?
-- A multimeter doesn't -do- anything; a multimeter shows you what is happening. But to use a multimeter correctly, you first have to know what it does. -Multi- means many, and -meter- is an indicator - it shows you something. Overall, a multi-meter shows you many things. A multimeter, though, can only show you one thing at a time...Read More
How Long does a Sealed Lead/Acid Battery Last?
-- The lifetime of a battery is affected by the remaining shelf life, its gradual loss of capacity, the temperature that the battery is stored at and used at, and the actual current used from the battery. Other less common factors are also involved, so the Amp/Hour Rating on a battery is not a hard and precise science...Read More
What Does E=IR Really Mean?
-- If it isn't just a word, and it isn't really something to be memorized in order to pass a test, what do the letters in Ohm's Law really mean?... Read More
What is "Power Limited?"
-- Whether it's a transformer, or it's a power supply of any type, it requires a stamp from a testing laboratory like UL, ULC, CE, FM, CCC, or other testing laboratory. The stamp means that the testing laboratory has tested it, found it to be safe, and put it on their...Read More
What's the Purpose of the Zener Diodes?
-- The circuit is just about the same as a Conventional Class B fire alarm circuit. The "control box" it's connected to looks like it has explosion detection devices also connected to it, and when explosion is detected, the control box closes a valve for people safety as well as property safety and protection...Read More
What are Pull-Up or Pull-Down Resistors?
-- Pull-up or Pull-down resistors are resistors whose job it is to pull and Integrated Circuit's (IC) input voltage either up to the power supply voltage, or down to circuit ground. The IC's input is usually high resistance; high enough that the moderate resistance on the Pull-up or Pull-down resistor acts like a short to the power supply (Pull-up resistor) or a short to circuit ground (Pull-down resistor)...Read More
Do Electrons Move or Charges Move?
-- I am teaching 4th graders. Everything in their materials show electricity flowing out the negative terminal of D-cells, through components such as wires, bulbs, motors and back into the positive terminal. My school district, formerly provided us with an answer key showing a similar circuit but had electricity flowing in the opposite direction. I just watched...Read More
How Can I be Better in My Field?
-- In any field of profession, whether a person can be "better" or not doesn't really depend on which books are best -over time that will change- or which school one goes to -most learning occurs after schooling-, but how a person does will depend on a person's -Attitude-...Read More
What is 24 VDC Filtered, Regulated, and Peak Voltage?
-- A power supply doesn't supply power - a power supply converts power. This is true of a DC power supply, and this is true of the utility power supplying power to the power supply. At the utility power generating station, they take the power that has been converted to steam, the power that has come from a dam across a river, the power that comes from wind, and then turn generators, creating the utility power. The power they generate...Read More
How do You Re-Surface Contacts?
-- Most of the contact surfaces I've worked with are either a solid material, like solid copper, solid copper alloy, or solid silver, or else they are plated, like copper plated with gold, copper plated with nickel alloy, or copper plated with silver. The plating, if used, is never really thick and can be scratched down to the sub-material if a hard substance like a file or screwdriver is used. Because...Read More
Does Replacing an Overheated Transformer Make the Power Supply Bad?
-- A transformer is made up of two coils of wire. The primary side and the secondary side. There are no other electrical components inside a transformer. The only way a coil of wire can get hot is that too much electrical current passes through the wires. Once in a great while, the windings inside the transformer can short out causing too much current to flow through the other wires, but that kind of internal short would probably burn out the fuse, or blow the circuit breaker. The original problem that caused...Read More
What is a Short on a Fire Alarm System?
-- For all electrical circuits, a short is a short-cut that the electricity is jumping across. Usually, a short is thought of as one wire touching another wire. The short accidently connects the wires together so electricity flows freely from one wire to the other. When the electricity flows freely from one wire to the other, the electricity doesn't... Read More
How Does One Connect RS232?
-- So two pieces of equipment can send data to each other, RS232 carries the data. When connecting the equipment using RS232, there's guessing the RS232 is wired correctly, and then there's knowing ... Read More
Why is the Sun's Corona so Hot?
-- The sun is a weighty subject. It is so weighty that its gravitational forces pull the atoms very close together. The atoms have speed, at least relative to each other, and being that close together, their electrons keep getting bumped off. This "bumped off" from all the individual atoms means the sun is made up of atom-nuclei...Read More