Fluke 87 Series Digital Multimeter - atraonline.com

1 Fluke 87 Series DigitalMultimeter:Tips, Tricks, and a Display FixFluke 87 Series DigitalMultimeter:54 GEARS August 2003 Fluke 87 Series DigitalMultimeter:Tips, Tricks, and a Display FixThe feature-packed Fluke 87series Multimeter s accuracy,versatility and durability haveestablished it as a standard for electricaltesting. Along with its sister meter, theFluke 88, this meter provides all sortsof functions and features that mosttechnicians never really become famil-iar with. So let s take a look at the Fluke87, and see how to get the most diag-nostic bang for the and TricksEver run the battery in your meterdead by forgetting to turn it off whenyou re finished with it?

2 Not the Fluke87; it comes with an Auto Power Offfunction, to turn the power off automat-ically after a couple minutes. You can disable the Auto PowerOff feature by holding the blue buttondown while you switch the meter on(holding any button down when turningon the meter will display all of the LCDsegments until you release the button). Disabling Auto Power Off is handyif you have to monitor a circuit for along time; otherwise, you can count onthe meter shutting off about a half-sec-ond beforethe torque converter clutchstarts shuttling. There are a few features you canenable by holding down other buttonsduring powerup; these are listed on theback of the let s examine a few of thefeatures and functions you can enablewith the meter already turned on:MIN MAXThe MIN MAX feature allows themeter to record and save the minimum,maximum, and average readings duringthe entire length of your test.

3 This ishandy for monitoring signals that maybe dropping out while you drive thevehicle, because the meter will storevoltage drops or spikes that you mightmiss while watching the display. You can cycle through the mini-mum, maximum, average and currentlymeasured values by pressing the MINMAX button repeatedly. Press the Hold button while inMIN MAX mode to freeze the readingson the meter; that way you can view thestored minimum, maximum, and aver-age values without them changing ifyou turn the key off, or if one of the testleads comes the button labeled PEAKMIN MAX below it (audible alert but-ton) while in MIN MAX mode will putthe meter into Peak MIN MAX will record minimum and maxi-mum voltage peaks that are much short-er than in regular MIN MAX.

4 Exactlyhow short depends on the age of yourmeter. Older Fluke 87 meters increaseThere s little doubt that a Digital Multimeter has become a sta-ple for today s transmission technician. Problem is, there are dozensof different meters out there, offering all sorts of different functionsand features, and at prices that range from a few bucks to severalhundred dollars. Which meter is right for you?To help you answer that question, we ve begun to look at a num-ber of Digital multimeters on the market. We ll examine their func-tions and features, to provide you with the information you need forchoosing your next is not endorsing any one meter or manufacturer over anyother; the meter you choose should be based entirely on your per-sonal requirements.

5 The purpose of this article is strictly to provideyou with a critical evaluation of the Fluke 87, to help you make anintelligent and educated Mike Van 7/9/03 5:07 PM Page 54the sampling rate to 1/1000thof a sec-ond; later meters are 4 times faster,recording at a speed of 250 microsec-onds. That s considerably faster thanthe normal 1/100thof a second in nor-mal MIN MAX mode. Peak MIN MAXmode will display the positive and neg-ative peak values of an AC RangingThe RANGE button allows you toselect a voltage or resistance rangemanually, so the meter won t swing inand out of range flashing OL andspiking the bargraph while you remeasuring a varying signal.

6 You shouldusually select the lowest range for ameasurement without going overrange(OL on the meter display means out oflimits, or overrange).Relative ModeThe REL (Relative) button willzero the meter at a particular measure-ment (this button has a little triangle, or delta symbol on it). The meter willthen display the difference between thestored value and the value being meas-ured. This is handy for zeroing themeter to measure low resistances moreaccurately. With the meter set to measureresistance, hold the test leads together,press the REL button, and the meterwill zero. This compensates for theresistance of the test leads.

7 Look for thelittle triangle on the left side of the dis-play to indicate that this function isactive. For more on this, check out thearticle on measuring resistance in theJanuary-February 2003 issue ofGEARS. The REL function can also be usedto compare voltages, so watch out: Ifyou accidentally press the REL buttonwhile you re measuring voltages, youmay end up with readings that don tmake and Duty CyclePressing the Hz button with thedial set to AC or DC voltage will dis-play the frequency of a signal in Hertz,or cycles per the correct voltage for thesignal you re measuring before enter-ing the frequency mode.

8 Set the selec-tor to AC Volts for AC frequency sig-nals, such as a G4 AEL or other type ofAC pulse generator, or to DC Volts forDC frequency signals, such as an EPCsolenoid signal. Press the Hz button a second timeand the meter will display duty Fluke 87 is an electronicsmeter; that is, it was built specificallyfor the electronics industry, not theautomotive industry. On this type ofmeter, duty cycle always comes onmeasuring the positive part of the sig-nal. This is what you d want for meas-uring a feed-controlled signal; that is, acircuit that receives a constant ground,while the power feed cycles on and can confirm that this is what themeter s displaying by looking for the + on the lower left side of the automotive duty cycled sig-nals are ground controlled; that is, theyreceive power all the time, and theground cycles on and off to energize thecircuit.

9 To measure the duty cycle onthese signals you ll have to switch to a negative duty cycle. Press the buttonlabeled PEAK MIN MAX (audiblealert button) to switch to a ground-con-trolled duty cycle measurement. Theicon on the lower left side of the displayshould switch to a negative ( ) is one of the major differencesbetween the Fluke 87 and Fluke 88. TheFluke 88 is a dedicated automotivemeter, so when you select duty cycle, itcomes on set to measure a negative duty Peak of FrustrationOne important thing you want tonote when checking pulse width modu-lated solenoid signals is measuring dutycycle percentage with a Digital multi-meter is not always accurate, especiallywith a peak and hold type of solenoidcontrol system.

10 Figures A and B showNissan EPC solenoid peak and holdwaveform on an oscilloscope at mini-mum and maximum duty cycle, respec-tively. Note that when you compare theminimum and maximum duty cyclewaveforms (figures A and B), the dura-tion of the peak portion of the wave-form does not change, it is the durationof the hold portion of the waveformthat varies and controls how long thesolenoid stays open. Some Digital mul-timeters will only recognize the peak and ignore the hold , and thereforedisplay a fixed duty cycle of about 15%that does not August 200355 Figure APeak and Hold Wave FormPEAK (Battery Voltage)NegativeVoltage SpikesPeak and Hold Wave Form0 VoltsMinimum Duty CycleFigure BPEAK (Battery Voltage)NegativeVoltageSpikes0 VoltsMaximum Duty CycleHold (3 Volts) 7/9/03 5:07 PM Page 55 The trick here is to use your meterto measure the DC voltage instead ofduty cycle.