ADT490 TroubleShooting Locating Opens B

2 Review a Circuit 2 Before we start to investigate a Trouble condition caused by a circuit fault, we should review how Fire Alarm circuits are designed and what makes a circuit NORMAL? To begin this discussion, we will make 3 assumptions: 1) The circuits will be CONVENTIONAL Fire Alarm circuits, as opposed to Addressable technology 2) The circuits will be arranged in the CLASS B style 3) The circuits will be of the INITIATING type and the SIGNAL type.

3 We will start with the Conventional, Class B, INITIATING circuit. What does it look like? Zn1 Zn2 Zn3 Zn4 Initiating Circuits The Class B-style Initiating Circuit consists of 2 conductors connected to the Fire Alarm Control Panel (FACP), Supply voltage on any INITIATING circuit is app. 24Vdc…. End of Line Resistor (EOL) is installed across the end of the circuit. This resistor provides a fixed current level referred to as “supervisory current”. Supervisory current flowing through the circuit is approximately 5mA, and will be slightly less or slightly more, depending on the value of the EOL. 5mA A Conventional Initiating circuit will be NORMAL when the correct level of supervisory current is flowing through it……. ….which means that the correct supply voltage is present… …and the correct EOL resistance is in place. Now we’ll take a look at this circuit with our Digital Multi-Meter (DMM). We can also say that when a Class B circuit is NORMAL, it will have a voltage source at one end and a fixed resistive value at the other.

44 When a Class B circuit is NORMAL, it has a voltage source at one end and a fixed resistive value at the other. Here’s sketch of Initiating circuit - but it is now “opened up” in the middle Zn1 Zn2 Zn3 Zn4 24 Vdc App. The EOL value has been fixed at 4.7KΩ A mA Com. V-Ω So imagine we are located in the middle of the circuit and with our DMM set to Volts DC, we connect our meter leads across the circuit wires that are coming FROM THE FACP…… Vdc …and we get expected reading of approximately 24 Vdc. What does this tell us? It tells us - circuit between us and the FACP is not open or shorted – which is good.

5 Now look “the other way” with our DMM – towards EOL. We set our DMM to read resistance Zn1 Zn2 Zn3 Zn4 24 Vdc App. 4.7 kΩ A mA Com. V-Ω 20KΩ 4.85 The reading is approximately the same value as the EOL. What does this tell us? It tells us that the circuit between us and the EOL is not open or shorted – which again, is good. The point of this exercise is that we can use our DMM to determine the “health” of the circuit.

66 Now we know that our DMM can be used to take voltage and resistance readings, in the middle of a conventional initiating circuit, to determine if the circuit is “normal”. Let’s take this a step further. Now, we’ll create a circuit fault, this time it will be an “open” – which means that a wire has broken or has become disconnected from a device. Let’s start with a circuit in the NORMAL state Let’s take our initiating circuit and extend it – it will make it easier to work on - and re-connect our EOL.

77 Now, populate circuit with initiating devices to resemble actual circuit as it is installed on a floor in a small apartment building Now we will pick a location at random on the circuit, and create an open... AC Power System Alarm System Trouble Zone 1 Zone 2 Zone 3 Zone 4 Batt. Ground Zn1 Zn2 Zn3 Zn4 …and our FACP will immediately display a Trouble condition, indicating an open circuit has occurred in Zone 1. All we know is that there is at least one Open Circuit fault on Zone 1. But we don’t know where it is on the circuit – that’s why we’re here! We know where it starts - and the EOL (let’s say it’s a 4.7KΩ resistor) indicates where the circuit ends.

Zn1 Zn2 Zn3 Zn4 To start, find (our best) mid-point of circuit, and open it by removing detection device. Imagine the device is smoke detector in apartment building corridor. Now take DMM, set to read VOLTAGE DC, and connect to pair of wires that we believe are coming from the FACP. A mA Com. V-Ω 25.3 Vdc It looks like we “see” the FACP from this location in the circuit, because we are reading the Voltage that is being supplied by the FACP. Conclusion: The Open is not between us and the FACP. Next, set our DMM to read RESISTANCE and connect it to the remaining pair – the pair that we believe is heading for the EOL. A mA Com. V-Ω ∞ But instead of reading the 4.7KΩ EOL resistor, we are getting a reading of infinity. Conclusion: The Open is between us and the EOL!

99 Congratulations! You have successfully completed the first step in performing a “Boolean Search”! “Boolean” refers to George Boole ( ) often referred to as the Father of Logical Thought. For our purposes, we are using the Boolean Truth Table approach to our Trouble Shooting routine. Here’s how it works:First, let’s go back to our conventional initiating circuit with the Open Circuit fault. Remember, we started our shoot at what we believed is mid-point of circuit.

Zn1 Zn2 Zn3 Zn4 A mA Com. V-Ω 25.3 Vdc A mA Com. V-Ω ∞ Looking towards the panel with our DMM set to read Vdc, we can see the voltage coming from the FACP – so this half of the circuit is “good”, i.e. True. And when we “look the other way” with our meter set to read Ω, we get Infinity – so this half of the circuit is faulted Open Circuit, i.e. False So what is our next move?

11 The Boolean Search routine now asks that we move to mid-point of the remaining (faulted) half of the circuit But first, we will carefully replace the smoke detector that we removed. Now we will move along the circuit towards the EOL, and open it up, this time by removing a heat detector …… ….and take the same meter readings that we did on our first shoot.

A mA Com. V-Ω 25.3 Vdc A mA Com. V-Ω ∞ From this new location, looking back towards the FACP, the circuit looks good. But the Open Circuit fault is still between us and the EOL Can you guess our next move?

13 Once again we find the midpoint of the remaining, faulted part of the circuit take another set of meter readings First, we carefully replace the heat detector that we removed. Then we remove the heat detector that is at the mid-point of the rest of the circuit A mA Com. V-Ω Now our meter readings have changed. 0.0 Vdc 4.7KΩ We no longer get a voltage reading which means the Open is now between us and the FACP. And when we look the other way we can now read the EOL resistor

Which means that the Open is between our last 2 shots – i.e. between the two heat detectors. Conclusion: The Open Circuit Fault is in the wiring coming to - or from - the smoke detector – or maybe in the detector itself. Are the Smoke detector LEDs flashing? In fact, the Open Circuit could be caused by the detector head not being twisted fully into its mounting base.

15

16 end of presentation