Fluke 189 user manual DB Measurements in AC Volts Functions, DBm Display

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Making Measurements

Measuring Voltage 3

dB Measurements in AC Volts Functions

The two ac volts functions allow you to display readings as deviations in dB (decibels) above or below an established level.

Set up dB measurements with the following procedure:

1.Make an ac volts measurement to be used as a reference point.

2.Press % to select dB. The dBm (or dBV) value appears in the primary display and the ac volts reading appears in the secondary display. A typical dB display appears in Figure 3-2.

3.Press % again to switch the ac volts and dB readings. Press % a third time to turn dB off.

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Figure 3-2. dBm Display

Normally, dB is measured as dBm, which is a measure of decibels relative to 1 milliwatt. The meter assumes a resistance of 600 Ω in making this calculation. This resistance can be set for any value from 1 to 1999 Ω , using the meter’s setup capabilities (see Chapter 5.) When set to other than 600 Ω the dBm reference resistance appears in the Index Display. (See Figure 2-4, item 17.)

Note

If dBm is displayed, check that the reference resistance value closely matches the impedance of the system being measured.

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Contents Model 187 Lifetime Limited Warranty Table of Contents Making Measurements Model 187Iii Specifications MaintenanceList of Tables Model 187 List of Figures Viii Safety Information Before You StartContacting Fluke WWarning Safety InformationBefore You Start International Electrical Symbols SymbolsGetting Acquainted IntroductionTurning the Meter On Automatic Power Off Battery ConsiderationsAutomatic Backlight Off Low Battery IndicationRotary Switch Rotary SwitchPushbuttons PushbuttonsBlue Key Function Rotary Switch Selections Position Rotary Switch FunctionView MEM Rotary Switch PositionsButton Pushbuttons Yellow Button Description Function Yellow Button Function Pushbuttons Button DescriptionSelecting the Range Understanding the DisplayPrimary Display Secondary Display Bar GraphDisplay Features Number Feature Display Features Description 8.8.8 Display Features NumberDisplay Features Description Number FeatureFMS8888 HM8888 8.8 Display Features Number 51000Input Terminals Using the Input TerminalsDisplay Hold and AutoHOLD Using Display HoldUsing MIN MAX Using AutoHOLDModel 187 Min Max Avg Using Fast MN MXUsing Hold with MIN MAX or Fast MN MX Using Relative Mode RELMeasuring Voltage Making MeasurementsAC Voltage Measurement Measuring AC VoltageDBm Display DB Measurements in AC Volts FunctionsBoth AC and DC Voltage Measurements Measuring DC VoltageAC and DC Display AC over DC DC over ACCapacitors before measuring resistance Measuring ResistanceOFF Automatically subtract this value Testing for ContinuityUsing Conductance for High Resistance Tests For in-circuit tests, turn circuit power off Conductance Measurement Measuring Capacitance Capacitance Measurement Testing DiodesDiode Test Measuring Temperature Shock, do not connect the thermocouples toElectrically live circuits Input Ranges Measuring CurrentMeasuring Current Input Alert FeatureFollowing are some tips for measuring current Measuring AC Current11. AC Current Measurement Measuring DC Current Current through one component Total current to circuit13. Functions Allowing Frequency Measurement Measuring Frequency14. Hz Display Measuring Duty CycleMeasures Negative Pulse Measures Positive Pulse16. Duty Cycle Display Measuring Pulse WidthStart and Stop on Negative Slope Start and Stop on Positive Slope18. Pulse Width Display Model 187 Logged Readings Memory Using Memory & Communications FeaturesTypes of Memory Saved Readings MemoryStoring Saved Readings Starting LoggingStopping Logging To avoid electric shock, disconnect the test Viewing Memory DataMEM View DisplayClearing Memory Using Communications 187Model 187 Selecting Setup Options Changing the Default SettingsOption Function Specific Setup SelectionsFactory Default PreconditionChoices Common Setup SelectionsAdjusting the Temperature Offset Changing the Default Settings Setting the Power Off Timeout Selecting Display Resolution 3 1/2 or 4 1/2 DigitsSetting the Line Main Frequency Setting the 24-Hour ClockSaving Setup Options Returning to Factory DefaultsMaintenance Introduction General MaintenanceTesting the Fuses Replace F2 if Replace F1 if Displayed Replacing the Batteries Battery and Fuse Replacement Replacing the Fuses User-Replaceable PartsCase of Difficulty MP8 MP9 Safety and Compliances SpecificationsPhysical Specifications Feature Summary Basic Specifications Detailed Accuracy Specifications KHz-100 kHz Accuracy Function45-1 kHz 20 kHzDC a 500.00 Ω Capacitance Diode Test MIN MAX AVG Burden Voltage A, mA, µA Frequency Counter SensitivityInput Characteristics