What is continuity test?

Salah satu tahapan terpenting sebelum melakukan comissioining mesin yaitu continuity test. Lebih lengkap silahkan baca artikel ini.

What is continuity?

You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means, are two things electrically connected. So if two electronic parts are connected with a wire, they are continuous. If they are connected with cotton string, they are not: while they are connected, the cotton string is not conductive.

You can always use a resistance-tester (ohmmeter) to figure out if something is connected because the resistance of wires is very small, less than 100 ohms, usually. However, continuity testers usually have a piezo buzzer which beeps. This makes them very useful when you want to poke at a circuit and need to focus on where the probes are instead of staring at the meter display.

For some basic circuits you can just look to see where the wires go to determine continuity but it's always wise to use a multimeter. Sometimes wires break or you're tired and can't easily follow all the PCB traces. I use continuity check all the time!

What is it good for?

Continuity is one of the most important tests. Here are some things it is good for

• Determine if your soldering is good. If your solder joint it is a cold solder connection it will appear connected but in actually it is not! This can be really frustrating if you are not experienced in visually detecting cold solder joints
• Determine if a wire is broken in the middle. Power cords and headphone cables are notorious for breaking inside the shielding, it appears as if the cable is fine but inside the wires have been bent so much they eventually broke.
• Making sure something isn't connected. Sometimes a solder joint will short two connections. Or maybe your PCB has mistakes on it and some traces were shorted by accident.
• Reverse-engineering or verifying a design back to a schematic

Remember!

You can only test continuity when the device you're testing is not powered. Continuity works by poking a little voltage into the circuit and seeing how much current flows, its perfectly safe for your device but if its powered there is already voltage in the circuit, and you will get incorrect readings

Always test to make sure your meter is working before starting the test by brushing the two tips together, and verifying you hear the beep. Maybe the battery is low or its not in the right mode.

Continuity is non-directional, you can switch probes and it will be the same.

If you are testing two points in a circuit and there is a (big) capacitor between those points you may hear a quick beep and then quiet. That's because the voltage the meter is applying to the circuit is charging up the capacitor and during that time the meter 'thinks' its continuous (essentially)

Small resistors (under 100 ohms or so) and also all inductors will seem like short circuits to a multimeter because they are very much like wires.

Likewise, continuity doesn't mean "short" it just means very very low resistance. For example, if you have a circuit that draws an Amp from a 5V supply, it will appear to be a 5Ω resistor. If you measure that with your meter it will think its a short circuit, but really its just a high-drain circuit.

Get into the mode

First step is to get your multimeter into the correct mode. Look for the icon that looks sort of like a 'sound wave'

Here are three examples. Note that sometimes the mode is "dual" (or possibly more) usage,

Turn the multimeter knob so that it points to this symbol

Touch and go

For a majority of multimeters, you're ready to go, just touch the tips of the probes together so that they make a beeping sound!

Here's a video demonstration

If you can't view embedded videos, click here to download an mp4

Here are some examples covering a couple of different multimeters

Example 1

This meter is very simple. When the probes are not touching, the display shows "1"

When you touch the tips together, the display changes to a three digit mode (it's displaying resistance, which we will cover later) It also emits a beep

Example 2

This meter is dual-mode but still very easy to use. Turn the dial to the symbol. When the probes are not touching the display shows "OL" which stands for Open Loop. (Open loop is another way of saying there is no continuity)

When you touch the probes, the soundwave icon shows up in the display (upper right) and it also shows a number. The number is not the resistance, actually...its the voltage (look for the V in the right hand side for Volts). This is because this mode is also a Diode Test (which will be discussed later)

Example 3

This meter is triple-mode and requires an extra step to get to the continuity function. Click on the image to get a closer view of the triple-mode. After you dial to this mode you must press the Mode button, the wave icon will then appear in the display.

You can see the wave icon in the top right as expected. This meter also displays OL (I've noticed that nicer meters do this)

Unlike the other meter, this one displays Ohms (see the symbol on the right of the display). The resistance is low (4.7Ohms) but not 0 (the ideal value) because the probes and wires act as resistors. Usually with these sorts of meters they will beep whenever resistance is under 100 ohms or so.

Probing a PCB

Here is an example of testing a PCB for continuity.The first test shows that the two points are not connected.

The second test shows that these two points are connected

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Why Use a Clamp Meter?

Mengapa mengukur Arus Listrik Menggunkan Tang Ampere?

Salah satu alat yang diperlukan pada saat kita melakukan commissioning dan pengujian arus listrik "test and run" mesin atau alat-alat yang menggunakan listrik lainnya dilapangan.

Clamp meters allow for measurement of current, without needing to disconnect the wires where the measurement occurs. By simply clamping the wire, you can get the measurement, and not cut the circuit. When using a multitester or a digital multimeter, the circuit has to be cut. In contrast, using a clamp meter, current can be measured by clamping a live wire over its sheath. In addition to its simple operation, it allows safe measurement of a higher current.

Clamp meters feature low internal resistance and have both a positive and negative lead. High current flow can indicate a short circuit, a defective component, or an unintentional ground. Low current flow can indicate high resistance, or poor current flow within the circuit. Both types of clamp meters (digital and analog) are designed to measure levels of direct current (DC) and alternating current (AC). Most products have built in sensors. Some clamp meters can test diodes or transistors while others can monitor thermocouples or resistance temperature detector (RTD) values. Some may adjust sampling rates automatically, display status information as a bar graph, and measure decibel (dB) readings. Our specialty clamp meters provide special measurement types and optional features. Some can test diodes or transistors. Others can monitor thermocouples or resistance temperature detector (RTD) values. Programmable clamp meters provide internal data storage and will allow you to establish activation triggers. Clamp meters are extremely useful and allow for many types of safe electrical testing.

Please visit Fluke Website for your information.

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Bagaimana Cara Menggunakan Multimeter

Using a Multimeter

A multimeter is used to make various electrical measurements, such as AC and DC voltage, AC and DC current, and resistance. It is called a multimeter because it combines the functions of a voltmeter, ammeter, and ohmmeter. Multimeters may also have other functions, such as diode and continuity tests. The descriptions and pictures that follow are specific to the Fluke 73 Series III Multimeter, but other multimeters are similar.

Important note: The most common mistake when using a multimeter is not switching the test leads when switching between current sensing and any other type of sensing (voltage, resistance). It is critical that the test leads be in the proper jacks for the measurement you are making.

Safety Information

• Be sure the test leads and rotary switch are in the correct position for the desired measurement.
• Never use the meter if the meter or the test leads look damaged.
• Never measure resistance in a circuit when power is applied.
• Never touch the probes to a voltage source when a test lead is plugged into the 10 A or 300 mA input jack.
• To avoid damage or injury, never use the meter on circuits that exceed 4800 watts.
• Never apply more than the rated voltage between any input jack and earth ground (600 V for the Fluke 73).
• Be careful when working with voltages above 60 V DC or 30 V AC rms. Such voltages pose a shock hazard.
• Keep your fingers behind the finger guards on the test probes when making measurements.
• To avoid false readings, which could lead to possible electric shock or personal injury, replace the battery as soon as the battery indicator appears.

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Input Jacks

The black lead is always plugged into the common terminal. The red lead is plugged into the 10 A jack when measuring currents greater than 300 mA, the 300 mA jack when measuring currents less than 300 mA, and the remaining jack (V-ohms-diode) for all other measurements.

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Range

The meter defaults to autorange when first turned on. You can choose a manual range in V AC, V DC, A AC, and A DC by pressing the button in the middle of the rotary dial. To return to autorange, press the button for one second.

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Automatic Touch Hold Mode

The Touch Hold mode automatically captures and displays stable readings. Press the button in the center of the dial for 2 seconds while turning the meter on. When the meter captures a new input, it beeps and a new reading is displayed. To manually force a new measurement to be held, press the center button. To exit the Touch Hold mode, turn the meter off.

Note: stray voltages can produce a new reading.

Warning: To avoid electric shock, do not use the Touch Hold to determine if a circuit with high voltage is dead. The Touch Hold mode will not capture unstable or noisy readings.

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AC and DC Voltage

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Resistance

Turn off the power and discharge all capacitors. An external voltage across a component will give invalid resistance readings.

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Diode Test

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Continuity Test

This mode is used to check if two points are electrically connected. It is often used to verify connectors. If continuity exists (resistance less than 210 ohms), the beeper sounds continuously. The meter beeps twice if it is in the Touch Hold mode.

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Current

Warning: To avoid injury, do not attempt a current measurement if the open circuit voltage is above the rated voltage of the meter.

To avoid blowing an input fuse, use the 10 A jack until you are sure that the current is less than 300 mA.

Turn off power to the circuit. Break the circuit. (For circuits of more than 10 amps, use a current clamp.) Put the meter in series with the circuit as shown and turn power on.

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Handbook of instrumentation and controls

MODUL 1 TEMPERATUR DETECTOR

RESISTANCE TEMPERATURE DETECTORS (RTDs)
Temperature
RTD Construction

THERMOCOUPLES
Thermocouple Construction
Thermocouple Operation

FUNCTIONAL USES OF TEMPERATURE DETECTORS
Functions of Temperature Detectors
Detector Problems
Environmental Concerns .

TEMPERATURE DETECTION CIRCUITRY
Bridge Circuit Construction
Bridge Circuit Operation
Temperature Detection Circuit
Temperature Compensation
MODUL 2 PRESSURE DETECTORS
PRESSURE DETECTORS
Bellows-Type Detectors
Bourdon Tube-Type Detectors
Summary
PRESSURE DETECTOR FUNCTIONAL USES
Pressure Detector Functions
Detector Failure
Environmental Concerns

PRESSURE DETECTION CIRCUITRY
Resistance-Type Transducers
Inductance-Type Transducers
Capacitive-Type Transducers
Detection Circuitry
MODUL 3 LEVEL DETECTORS

LEVEL DETECTORS
Gauge Glass
Ball Float
Chain Float
Magnetic Bond Method
Conductivity Probe Method
Differential Pressure Level Detectors

DENSITY COMPENSATION
Specific Volume
Reference Leg Temperature Considerations
Pressurizer Level Instruments
Steam Generator Level Instrument

LEVEL DETECTION CIRCUITRY
Remote Indication
Environmental Concerns
MODUL 4 FLOW DETECTORS

HEAD FLOW METERS
Orifice Plate
Venturi Tube
Dall Flow Tube
Pitot Tube .

OTHER FLOW METERS
Area Flow Meter
Displacement Meter
Hot-Wire Anemometer
Electromagnetic Flowmeter
Ultrasonic Flow Equipment

STEAM FLOW DETECTION

FLOW CIRCUITRY
Circuitry .
Use of Flow Indication
Environmental Concerns
MODUL 5 POSITION INDICATORS

SYNCHRO EQUIPMENT
Synchro Equipment

SWITCHES
Limit Switches
Reed Switches

VARIABLE OUTPUT DEVICES
Potentiometer
Linear Variable Differential Transformers (LVDT)
Summary
POSITION INDICATION CIRCUITRY
Environmental Concerns
MODUL 6 RADIATION DETECTORS
OBJECTIVES
RADIATION DETECTION TERMINOLOGY
Electron-Ion Pair
Specific Ionization
Stopping Power
Summary
RADIATION TYPES
Alpha Particle
Beta Particle
Gamma Ray
Neutron .

GAS-FILLED DETECTOR
Summary
DETECTOR VOLTAGE
Applied Voltage
Summary
PROPORTIONAL COUNTER
MODUL 7 PROCESS CONTROLS

PRINCIPLES OF CONTROL SYSTEMS
Introduction
Terminology
Automatic Control System
Functions of Automatic Control
Elements of Automatic Control
Feedback Control

CONTROL LOOP DIAGRAMS .
Terminology
Feedback Control System Block Diagram
Process Time Lags
Stability of Automatic Control Systems

TWO POSITION CONTROL SYSTEMS
Controllers
Two Position Controller
Example of Two Position Control
Modes of Automatic Control .

PROPORTIONAL CONTROL SYSTEMS
Control Mode
Proportional Band
Example of a Proportional Process Control System

RESET (INTEGRAL) CONTROL SYSTEMS
Reset Control (Integral)
Definition of Integral Control
Example of an Integral Flow Control System
Properties of Integral Control

PROPORTIONAL PLUS RESET CONTROL SYSTEMS
Proportional Plus Reset
Example of Proportional Plus Reset Control
Reset Windup

PROPORTIONAL PLUS RATE CONTROL SYSTEMS
Proportional-Derivative
Definition of Derivative Control
Example of Proportional Plus Rate Control
Applications

PROPORTIONAL-INTEGRAL-DERIVATIVE CONTROL SYSTEMS
Proportional-Integral-Derivative
Proportional Plus Reset Plus Rate Controller Actions

CONTROLLERS
Controllers
Control Stations
Self-Balancing Control Stations

VALVE ACTUATORS
Actuators
Pneumatic Actuators
Hydraulic Actuators
Electric Solenoid Actuators
Electric Motor Actuators

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Instrument Engineer's Handbook

Bela Liptak's acclaimed "bible" of instrument engineering now enters its fourth edition with fully globalized coverage, an outstanding panel of international contributors, and major additional coverage that reflects the advances made over the last decade since publication of the third edition. Expanded coverage includes descriptions of overseas manufacturer's products and concepts, model-based optimization in control theory, new major inventions and innovations in control valves, and a full chapter devoted to safety. The book also covers the transmitters, controllers, valves, regulators, actuators, dampers, and other drives that have been introduced since the previous edition.

Rincian lebih lanjut

Instrument Engineers' Handbook: Process Control and Optimization

Oleh Bela G. Liptak

Diterbitkan oleh CRC Press, 2005

ISBN 0849310814, 9780849310812

2464 halaman

BACA? Klik Disini!

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