7
\$\begingroup\$

What does the horizontal bar indicate and how to use it in my measurement?

photo of DMM display

\$\endgroup\$
  • 4
    \$\begingroup\$ what have you observed about the bar? \$\endgroup\$ – jsotola Feb 13 at 6:33
  • 15
    \$\begingroup\$ That horizontal bar means your Fluke 87 is defective and you should send it to me, immediately. I'll replace it with a Regal DT830B right away! -- Not really. That's a joke. The horizontal bar there just means a "% of scale." You can see the "6" there? The 2.3 reading is about that % of the 6 V scale. You are in "auto-ranging mode." You really should read the manual. ;) \$\endgroup\$ – jonk Feb 13 at 6:33
  • \$\begingroup\$ @Jonk Sir, then it will help to read the voltage properly (average reading) if the votlage is fluctuating in Volts.. say jumping from 2 V to 4 V, for example.. am I right? \$\endgroup\$ – Sonder Feb 13 at 7:06
  • 1
    \$\begingroup\$ @Sonder You should also buy an analog meter for such things. I'd recommend something cheap but good: a TekPower TP7040. There are advantages to having an analog meter for some cases (such as the one you may be talking about.) And the unit is quite cheap (about 1/20th the price of the Fluke you have.) To see why, set up a signal generator to provide a sine wave at \$1\:\textrm{Hz}\$ that varies from about \$3\:\textrm{V}\$ to about \$7\:\textrm{V}\$. Then try and use the Fluke 87 and then also the TP7040 on the signal. You'll see quickly why you want an analog, also. Worth a few extra to have. \$\endgroup\$ – jonk Feb 13 at 7:18
  • 3
    \$\begingroup\$ But if you find RMS is too wonky, jonk will accept trade-ins to analog \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 13 at 10:47
17
\$\begingroup\$

That bar at the bottom of the screen simulates an analog meter - the length of the bar increases with increasing digital readings. It is often easier to observe a varying voltage by looking at the bar than trying to interpret rapidly changing digits.

\$\endgroup\$
14
\$\begingroup\$

From the Fluke 87V datasheet page 11 point 18 :

The number of segments is relative to the full-scale value of the selected range. In normal operation 0 (zero) is on the left. The polarity indicator at the left of the graph indicates the polarity of the input. The graph does not operate with the capacitance, frequency counter functions, temperature, or peak min max. For more information, see “Bar Graph”. The bar graph also has a zoom function, as described under "Zoom Mode".

\$\endgroup\$
  • 1
    \$\begingroup\$ The +1 from me will be visible after I gather some points. Thanks. \$\endgroup\$ – Sonder Feb 13 at 7:44
14
\$\begingroup\$

The bar is a fast-responding 'analog meter', that can be useful for following variations in the input voltage, for instance when you're adjusting a circuit with a potentiometer in real time.

In the Fluke I had, the digital display updated once per second to 3200 count resolution, while the 32 step bar updated at 25Hz.

This was introduced shortly after DMMs were to counter the criticism that analogue meters were better when you had a varying input and could watch the needle swing in real time. Waiting a second for the digits, and then needing to think what they meant, makes tuning circuits unnecessarily awkward.

\$\endgroup\$
  • \$\begingroup\$ Your last paragraph is the best answer \$\endgroup\$ – User323693 Feb 13 at 14:56
2
\$\begingroup\$

I know this question has been answered, but I don't agree with the answer.

The horizontal bar shows you how much of your current range you have used up, ie. how much the voltage/current/whatever can change before the meter has to switch to a higher input range

Anyone who has spend hours upon hours using a multimeter will understand why this is usefull; sometimes when you are measuring for instance a voltage with a multimeter what you are measuring might be very close to the upper bound of one range, and so it can happen, at least with some older multimeters, that the range selection will start toggling between two ranges, which can be super annoying. If you are measuring something which you know has spikes that are larger than what you are trying to measure then the horizontal bar will give you an indication of whether the spikes that can occur will be likely to cause the multimeter to change range while you are measuring, letting you change to a higher range if what you are measuring is close to saturating the value of the horizontal bar..

Without the horizontal bar you can have no way of knowing, by just looking at the reading from the multimeter, how much of the current range you are using.

The bar is also useful in the case that you are using manual range, because it may tell you that what you are measuring is only using up a small part of the current range, ie. you are not getting the full resolution of the instrument, knowing this you can turn down the range to use up more of the range of the instrument for you measurement and hence get better resolution.

Several of the answers here claim that it is for DMMs to "compete" with analog meters. I very much disagree with that, DMMs are inherently faster than analog meters, although you might not be able to rapidly read the changing numbers on the display, there is a physical limit to how fast the nedle on an analog meter can move as well, and it is driven by a coil which futher limits its bandwidth. Besides, looking at the bar moving back and forth might let you know the voltage is changing, but not by how much, as you have no way of knowing how large a value a certain size of bar corresponds to. And besides; You're an idiot if your trying to measure a changing voltage (other than pure AC) using a multimeter rather than an oscilloscope.

\$\endgroup\$
  • \$\begingroup\$ Vinzent, I have often used a multimeter to measure changing voltage using a multimeter when an oscilloscope was not available and Im not an idiot. \$\endgroup\$ – Transistor Feb 15 at 10:06
  • \$\begingroup\$ @Transistor I didn't mean to offend anyone with that statement, you're obviously not an idiot for using what is available to you, I meant it more in the sense that if you intentionally use the multimeter rather than an oscilloscope because you think that bar is good enough for that job in general, then you're likely making a mistake.. that sayed some people choose to get offended, some don't. \$\endgroup\$ – Vinzent Feb 15 at 10:12
0
\$\begingroup\$

Digital multimeters have measurement ranges like 0-200 mV, 0-2V, 0-20V, 0-400V etc.

Bar graph shows how near you are to the end of one range.

\$\endgroup\$
  • \$\begingroup\$ Maybe saying that "the bar graph shows an analogue reading relative to full scale" might be a better way of saying it. \$\endgroup\$ – Transistor Feb 15 at 10:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.