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Analog Meter

Discussion in 'General Electronics Chat' started by windozeuser, Sep 7, 2005.

  1. windozeuser

    windozeuser New Member

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    Hey, I'm just intrested in knowing if the old Analog multimeters are still useful.

    Please list popular uses and why it's surperior to Digital ones.

    I thought Digital was more accurate than analog. The only thing I can think of is that Analog would be more sensitive?
     
  2. Electrix

    Electrix Member

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    One application where (Old) Analog Meters are useful are in Bridges. Wheatstone Bridge arrangment used for Calibirating and Standardising Resistors, Capacitors employ the deflection type meter to show the null point or degree of exactness.
     
  3. Sebi

    Sebi New Member

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    Both type can be sensitive and accurate. The digital types eliminate the parallaxis-failure, but with inaccurate voltage divider sometimes wronger as a good analogue with mirror-scale.
    The good point for analog: the pointer can follow 0.01...1sec voltage changes. This is the cause why have most digital multimeter also bargraph-scale.
     
  4. dave

    Dave New Member

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  5. Dean Huster

    Dean Huster Well-Known Member

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    This is a LONG post. Here's an article for some curriculum I wrote that pretty well covers this subject.


    VOMs, VTVMs and DMMs

    You have a lot of choices when it comes time to purchase your first measuring instrument. Your first instrument will most likely be one that measures voltage and resistance and will be in the form of a volt-ohm-milliammeter (VOM), digital multimeter (DMM) or vacuum-tube voltmeter (VTVM). There are a few other variations on these meters. The solid-state equivalent of the VTVM is the transistorized voltmeter (TVM). A very accurate VTVM that was usually only found in calibration labs is called a differential voltmeter (I'll use the abbreviation DVM in this article, which in other writings could otherwise mean "digital voltmeter"). The RF (radio frequency) voltmeter is used for high-frequency ac measurements and is a rather delicate and expensive piece of equipment. Finally, the ac voltmeter (ACVM), which also has a very limited function, is often found in audio labs and audio service shops. A multimeter has many measurement functions, and as such, compromise must be made. The more functions a meter has, the more likely it is that the meter will have less accuracy or single-function capability overall as compared to a meter designed to measure only one parameter. More on that later.

    What should you buy? What are the advantages and disadvantages of each type of meter? Some folks will tell you that anything but a DMM is foolish. It's the newest, best, most accurate, most dependable, etc. meter you can get, according to them. Not necessarily so. Let's take a
    look at each of these meters and help you make an informed decision.

    First of all, your choice is to buy a new meter or a used meter. If you're buying new, you're going to be limited to selecting between a VOM and a DMM. Other than solid-state versions of the ACVM, they don't make the other instruments any longer. For the most part, they've all been replaced by the DMM. If you're buying used, you have a lot of types of instruments from which to choose.


    VOM, or Volt-Ohm-Milliammeter

    During the 1960s and 1970s, VOMs were often called multimeters because they were capable of being configured for multiple functions. A typical VOM will measure dc and ac voltage, dc current and resistance. A VOM requires no external power for operation other than when it's measuring resistance. Even with a dead or missing internal battery, all but the resistance function of a VOM will be useable. A VOM never requires connection to external power. So there is the first advantage of a VOM: while a DMM with a dead battery is good only for a paper weight, a VOM will still be useable for a variety of tasks.

    The average industrial VOM will measure from a few tenths of a volt dc or ac, up to 1000 volts or more. They'll measure direct current from the low microamps to as much as 10 amperes. Resistances from a few tenths of an ohm to around 20M ohms can be measured. Of course, different manufacturers and different models will have various differences in function and range. VOMs that can measure ac current just don't exist other than the more specialized clamp-around types such as the Amprobe brand. A typical Amprobe VOM can measure ac voltage on three ranges,
    resistance on one range and ac current on maybe five ranges. Resistance and voltage is measured using the typical VOM-type probes while the ac current is measured by clamping the jaws of the meter around the conductor through which the current is flowing. Amprobes are used almost exclusively by industrial electricians who have to deal with electric motors and 3-phase power. But Amprobes typically don't measure dc parameters.

    A VOM has a lot of disadvantages when compared to other meters. Its accuracy compared to a DMM is not that good. The best VOMs have accuracies of anywhere from ±1% to ±3% while the worst DMM has an accuracy of ±0.5% and better DMMs boast something more like ±0.1% or better. However, that doesn't mean that the VOM won't work for you. When you're troubleshooting, it's rare than you need the accuracy of a DMM. Usually, you're looking to see if a voltage is there at all or if it's within some ballpark value. The DMM accuracy is needed only if
    you're an experimenter who's designing a circuit such as an attenuator, digital-to-analog converter or some metering circuit where you need to accurately check a voltage or resistance. That's not done very often.

    Another disadvantage of a VOM is the fact that most are rather delicate. A VOM uses a mechanical meter movement to indicate the measured quantity and these are manufactured with the same precision as fine clockwork. Dropping a VOM can destroy the movement by cracking
    the jeweled mounting pivots, bending the movement axle or smashing the meter glass to smithereens. Most older VOMs are made with Bakelite cases, and they can crack into a lot of pieces when dropped onto concrete.

    Newer VOMs with current safety standards are limited to 1000v maximum. Older VOMs were usually available with a 5000 volt range. Most DMMs cannot measure much more than 500 volts safely. Better VOMs are capable of measuring as much as 10 amps on their current range while most DMMs are limited to no more than 2 amps. A VOM can only measure dc current while a typical DMM can measure dc and ac current.

    The Simpson 260 is by far the most famous and most common of all VOMs, although other models were made by Triplett (the model 630 was most common), Beckman and a host of other U.S. and Asian manufacturers. Several of the old kit manufacturers such as Knight-Kit and Heathkit made VOMs in kit form. New prices vary from around $10 for a Wal-Mart VOM that will not serve you well, to a Simpson 260, Series 8 that costs around $200. You can get used Simpson 260s on ebay and other on-line auctions for a lot less, but you have to be careful or you'll get one that's pretty much wrecked. But Simpsons are still supported by Simpson Electric and parts are easily available. The Simpson 260 began with the Series I, then went to the II and the III. After that, they used Arabian numerals, going to the Series 4, 5, 6 and 7. Series 8 is the current model being sold. Some parts are interchangeable among the series, but most are not. There have been a lot of range, jack and battery voltage changes and within each series, there have been several models. For instance, a Series 5 would be a plain meter, while a 5M had a
    mirrored movement and a 5P had electronic meter protection.

    Usually, a VOM will load a circuit down more than a DMM, especially when measuring ac voltage. A typical DMM has an input resistance of 20M ohms. A VOM's input resistance when measuring voltage is rated as so many ohms per volt. Commonly, a VOM will be rated at 20K ohms/v on the dc voltage ranges, although some inexpensive meters were rated at only 1K ohms/v. On a 2.5v range, a meter with 20K ohms/v sensitivity will have an input resistance of 20K ohms multiplied by the maximum voltage on the range, or (20K)(2.5) which is 50K ohms. That's a lot lower than a DMM. On the 1000v range, a VOM will have an input resistance of (20K)(1000) or 20M ohms, the same as a DMM. However, an older meter with a 5000v range will have an input resistance of 100M ohms on that range.

    So, far, it would appear that a 20K ohms/v VOM has nothing but disadvantages, but that's not entirely true. While a DMM is far more accurate than a VOM, there are times when a VOM will provide more accurate readings over a DMM. A 20K ohm/v meter may give a more accurate voltage reading than a DMM if you're measuring high voltages in high-impedance circuits. Let's suppose that you're trying to measure 1000v in a high-impedance circuit. That older meter with the 5000v range and its 100M ohm input resistance will load the circuit down a lot less than that 20M ohm DMM, so the voltage will read more accurately on the VOM even though the DMM may be specified with more accuracy. The analogy might be that a Corvette can go faster than a Freightliner road tractor in most cases, but not if they're both towing 50,000 pounds!

    Although it was stated as a disadvantage from a damage point of view, another advantage to a VOM is the fact that it's an analog meter, using a mechanical movement to indicate the reading. If you're using the meter to adjust a circuit for a maximum or minimum voltage, it's a lot easier to
    see that maximum or minimum on the swinging pointer of an analog movement than it is to try to watch a bunch of digits on a DMM jitter around as the voltage is adjusted and the meter samples that voltage. I can use a VOM to peak or null a voltage (that's what we were just doing) or to set a power supply to a certain voltage a lot faster with a VOM than I can with a DMM. Now, the final setting may not be more accurate, but in most cases, it will be close enough and the speed at which the adjustment is done more than makes up for the small difference in final overall accuracy. If a person is doing alignments on older radio communications receivers, they'll use an analog meter at the receiver output rather than a digital meter, since they'll be making upwards of 10 to 50 adjustments while watching the meter. Any savings in time on a single reading will
    definitely pay off on the overall time spent on the complete alignment.

    That same analog movement of a VOM makes it less sensitive to outside disturbances than a DMM. DMMs are nearly useless when used around a radio transmitter because the RF signal often gets into the meter from the outside and messes around with the electronics, while it has no effect on the "lowly" VOM.


    DMM, or Digital Multimeter

    A DMM is available in two varieties, the handheld version or a bench version. The handheld version is most popular because of its usually lower price and the convenience of its portability. Some bench versions need connection to the power mains (usually 120 vac in the U.S. or 240 vac in the U.K.), while some less-expensive models are just physically larger versions of the handheld units and have their own internal power source, usually in the form of a covey of "D" cells.

    Digital multimeters, by their very nature, are more accurate than nearly any other analog meter. Because of the mass-production of highly accurate integrated circuits that were unavailable 20 years ago, DMMs are now less expensive and more accurate than earlier models. Most DMMs are able to measure dc and ac voltage, dc and ac current and resistance. The lousiest DMM may have a basic dc accuracy of ±0.5% and I have seen some ±1% boxes that were made back in the 1970s. Today, DMMs typically have accuracies of around ±0.2% or better, many being closer to ±0.1% or ±0.05%. However, once you move off the basic dc voltage
    range, the accuracy typically gets worse. DC current on good meters made by Fluke, Hewlett-Packard (now Agilent) and Tektronix may have dc current accuracy as good as their dc voltage accuracy because they use laser-trimmed shunt resistors. But most imported meters will have less
    accuracy when measuring current. All DMMs have worse accuracy when measuring ac voltage or ac current and even worse accuracy yet when measuring resistance. A meter than has a basic DCV accuracy of ±0.1% may have an ACV accuracy of ±0.5% or worse and as the frequency
    goes higher, so does that accuracy percentage. The resistance ranges of that same meter may be upwards of ±1.5%. These inaccuracies are caused by the fact that extra circuits must be inserted into the circuitry to convert ac voltage or resistance to a dc voltage that the digital metering
    circuitry can handle. These extra circuits contribute a lot of error to the overall measurement. Still, DMMs are more accurate than most analog meters.

    There are more brands of DMMs out there than any other instrument. They come from the U.S., Europe, Japan, Malaysia, Korea, the R.O.C. and China. An Asian import may get any one of six different "brand" names affixed to it here in the States. Your best brands will be names like
    Fluke, Hewlett-Packard (Agilent), Tektronix, Beckman and Keithley. Some of the most accurate bench meters are made by Agilent. Fluke has the largest variety of handhelds. If there was one brand that was better than any other for general purpose use, it would be Fluke. Fluke DMMs are considered to be nearly "bulletproof" in that they can be abused like no other meter and come out working just fine. You can accidentally have it set on the OHMS or AMPS function and try to measure ACV from a wall receptacle and the worst thing that will happen is a blown fuse. Other
    brands, especially the Asian imports, will often be destroyed doing something like that. Fluke meters are also rated for Category III or IV measurement situations. This means that you can use them to measure voltages at the service panel where there's high-energy 460v 3-phase without worry. Lesser meters will often explode (yes, EXPLODE, as in, take your head off, and that's no exaggeration) in a technician's hands under those conditions.

    Because there are no critical mechanical parts, a DMM is usually more durable than a VOM. A good Fluke DMM with its rubber cradle can take some pretty ferocious drops onto concrete and not be phased in the least. Being all-electronic, a DMM can take overloads on its ranges that
    would otherwise bend the pointer of a VOM.

    A DMM isn't perfect. One of the biggest flaws of a DMM is the fact that the display often resolves more digits that the internal electronics can provide. This means that a DMM displaying 5 digits of reading with an accuracy of ±0.1% is lying to you. Those last two significant digits on
    the display are likely not accurate. Those least-significant digits may be OK for observing short-term changes in a reading, but not for what is known as a quantitative measurement. And if you move to a function such as ACV or OHMS that has an even greater amount of slop in the
    specifications, the display is even less reliable. A 3-1/2 digit display resolves to about ±0.1%; a 4-1/2 digit display resolves to about ±0.01%. But it's rare to see a 4-1/2 digit meter that has a specification much better than ±0.1% to ±0.05% at best on the DCV ranges.

    Anymore, DMMs often come with more than just the basic E-I-R measurement functions. Some add functions for measuring capacitance, inductance and frequency as well as diode and transistor testing functions.

    If there is one use of a DMM that can justify its purchase, it's the fact that it can be an inexpensive secondary voltage and resistance standard for you. A DMM is more than 4 times (often more than that) accurate than an analog meter such as a VOM or VTVM. You can use comparative measurements of a DMM to calibrate a VOM or VTVM. If this is your primary use for the DMM, then I'd look to getting the most accurate one that you can afford, going for the best accuracy on the basic functions rather than going for a lot of extra functions.


    VTVM, or Vacuum-Tube Voltmeter

    The VTVM has been around a long time, beginning in the 1930s and having several revisions and updates as the years went along. A VTVM puts an amplifier between the meter and the test leads of a VOM, giving the meter extended ranges and a high input resistance. The input
    resistance of most VTVMs is around 10M ohms. The original VTVMs used the large vacuum tubes of the day, while the more recent service-grade models finally settled on a nearly universal design and circuit using a 12AU7 as the amplifier and a 6AL5 as the rectifier for the ac ranges. Later
    VTVMs were primarily made for the television service industry and had dual scales on the meter movements that gave ac voltage readings in both rms (root-mean-square) and peak-to-peak (p-p) values. The rectifier circuit in the meters read the peak value of the input waveform so that p-p (double peak) displays were valid. Since oscilloscopes displayed their voltage readings in p-p units, and most television schematics gave waveforms in p-p units, the VTVM readings were
    compatible.

    A VTVM has extended ranges, the lowest usually being 1.5v full-scale (0.5v full-scale on some better models) to 1500v full-scale. They measured dc and ac voltage and resistance. A VTVM cannot measure current, but since current measurements are both rarely needed and
    difficult to make, that function is hardly missed. What the VTVM leaves off in current capability is made up for on the resistance ranges. Even the most rudimentary VTVM is capable of measuring resistance values up to 1000MW!

    A VTVM has the one disadvantage of having to be plugged into the ac mains to operate. Even at that, for some reason most VTVMs still used a single 1.5v "C" cell for the resistance function rather than deriving this voltage from the ac mains supply. Owners of VTVMs often forget about this little battery in their meters until it's too late and it has already leaked chemicals over critical parts in the meter.

    Probably the most famous of all VTVMs is the RCA VoltOhmyst series of meters. While most VTVMs used three probes (common, ac/ohms, dc) for their various functions, the VoltOhmyst and some EICO models used a "Uniprobe" that put the ac/ohms and dc probe in the same probe. On any other VTVM, the main difference between those two probes is the fact that the ac/ohms probe lead is a simple, unshielded piece of test lead wire while the dc lead is a piece of shielded coaxial cable with a 1MW resistor installed in series with the center conductor at the probe end of the cable. A "Uniprobe" is made using the coaxial cable as the main conductor. A
    slide switch on the side of the probe switches between the two probe functions, "AC/OHMS" and "DC", by shorting out the resistor in the AC/OHMS position. Although this single probe was considered to be a great convenience to most folks, it added a nasty operator trap. Often, the technician would forget to slide the probe switch to the correct setting for the function to which he'd set the VTVM. If trying to measure low resistance values, the error might be obvious. But some ac or dc measurements might be off a considerable amount, but not by enough that it would be noticed as an error. Because of that trap, I've always preferred the VTVM with three separate leads rather than just two.

    The VTVM offers most of the advantages of the VOM with the enhancement of the resistance ranges and input resistance. Otherwise, accuracy is about the same. A VTVM is a little more difficult to use than a VOM because you have to be sure that the ZERO ADJUST knob is tweaked fairly often to insure that the pointer rests at zero with the probe leads shorted. The amplifier in the unit can cause drifting of the zero point as it warms up. The VTVM that is left on all day usually has little drift after the first hour's warmup. And, of course, you're tethered to the wall with the VTVM.

    In the 1960s, there was one or two projects in the electronics hobbyist magazines for making VTVMs (DCV only) that were battery operated, although still using vacuum tubes. These projects tried to make an instrument that provided the high input resistance of the VTVM in a
    battery-operated, handheld unit. I don't know of any meters of this type that were ever commercially available.

    A VTVM will need some periodic calibration. Inside will be three or four calibration adjustments for basic dc accuracy, ac accuracy and balance. If tubes are changed or new tubes have aged, these adjustments may have to be touched up.

    You might think that a VTVM, with its complement of tubes, might be less reliable than a VOM. That isn't always true. The Knight-Kit KG-620 that I purchased as a kit when I was a kid in high school in the mid-1960s has never need a single repair in the 40 years that I've had it, and I still use it to this day. I did make a circuit that runs off the heater supply to the tubes to replace the OHMS function battery. It probably wouldn't hurt if I were to update the VTVM a bit by replacing the old selenium rectifier with a new silicon rectifier and replacing the aged power supply filter electrolytic capacitor with a new one. Electrolytic caps do deteriorate with age and heat.

    My Knight-Kit KG-620 was my first kit and my first test instrument, and it was a VTVM. I'm glad I bought the VTVM first. If I already had a VOM, I'd probably have waited a long time before getting a VTVM, if I ever did. This way, I had the functionality of the VOM with the tremendous advantages of the VTVM. Of course, I eventually ended up buying a VOM, the 20K ohm/v Knight-Kit model, and later a cheaper 20K ohm/v Micronta from Radio Shack. I'd still recommend that a person get a VTVM first rather than a VOM or DMM.

    VTVMs aren't made anymore. If you want one, you'll have to search ebay or some other source to find one. While you're at it, you might as well find two or three that are just alike in case you need parts to get one going. Hangar queens will be the only source of special parts that you'll have.

    So far, I've only been referring to what are known as "service grade" VTVMs. There are lab-grade VTVMs as well, and these are just as valuable and useful ... and just as inexpensive to buy on the surplus market. Hewlett-Packard made the 410B which has all the standard VTVM
    functions. In addition, it has a special ac probe that has the rectifier tube built right in. Because of that, the 410B is capable of measuring ac to frequencies extending to over 100 MHz. They also made the 412A, a similar instrument without the extended ac frequency capability.


    TVM, or Transistorized Voltmeter

    The TVM is nothing more than a solid-state version of the VTVM. Most TVMs are exact functional duplicates of VTVMs with the advantage of battery operation so that you don't need to have the meter plugged into the mains all the time. Some units had rechargeable batteries. They
    still have the zero adjust knob to account for amplifier drift. The TVM wasn't on the scene very long before the DMM shoved it aside.

    The average TVM is a "service grade" instrument. For lab-grade work, Hewlett-Packard made the 410C, a solid-state upgrade to their original 410B, also with the ac rectifier in the probe head for high-frequency measurements. After being operated for several hours, it's still surprising
    to find that the ac probe head is warm to the touch because of the heater in that little rectifier tube. I consider the 410C to be one of Hewlett-Packard's finest meters.


    ACVM, or AC (Alternating Current) Voltmeter

    The ACVM is a specialized instrument that is designed to measure only one thing: ac voltage. And it was designed to do this well. The average multimeter, whether VOM, VTVM or DMM, has limited capabilities when measuring ac voltage. The ACVM overcomes these limitations at the disadvantage of having only one function.

    The average multimeter measures ac voltage fairly well, as long as the voltage is at least 0.5 v or more and that the frequency isn't much above 1 KHz. A lot of otherwise fine DMMs loose significant accuracy when the frequency of an ac voltage gets over 1 KHz and they start to seriously cough and sputter when the frequency gets over 10KHz. So, compared to a common DMM, an ACVM measures lower values and at higher frequencies. Now, there are some DMMs, such as the Tektronix DM501, that have attenuator compensation adjustments to allow them to
    measure frequencies into the megahertz realm. Still, they lack a low-amplitude measurement capability.

    A good ACVM will have ac voltage ranges from 0.001 v (1 mv) full scale up to 300v full scale. Some even go as low as 300µv full scale. The frequency response of good ACVM made by Hewlett-Packard is as high as 10 MHz and as low as 4 Hz. Because of the broad range of voltages and frequencies that the meters will handle, they are excellent for audio work where voltage levels from phono cartridges and tape heads can be in the millivolt range and the voltage at the output of vacuum tube amplifiers can get into the hundreds of volts.

    The ACVM is the indicating instrument of choice at the audio output of communications receivers during alignment. It is also the main measuring instrument at the heart of a THD (total harmonic distortion) distortion analyzer. As a matter of fact, most distortion analyzers have the ability to use their internal meters as an ACVM to make the instrument more versatile. Most ACVMs have output jacks so that you can use the ACVM as an amplifier. The output jacks are also handy for connecting an oscilloscope to view the signal being measured since it can see clipping that the meter can't "see". You could team a DMM to an ACVM, using the ACVM for fast peaking or nulling and the DMM for a final "fine tune".

    The ACVM isn't a first-instrument-to-have purchase. You still need that VOM, VTVM or DMM for general-purpose measurement and troubleshooting. But if you do a lot of audio work, audio design or work on stereos and PA equipment or communications gear, the ACVM is an
    excellent investment. Commercial Asian imports are available new for around $150. Most of those have an upper bandwidth of about 1 MHz. Some of them are "dual channel", meaning that there are two concentric pointers on the meter movement so that you can observe two different
    measurements (e.g., input and output) simultaneously for less money that what two meters would cost. Of course, if that specialty meter movement ever goes bad, you're up a creek. For my money, I'd prefer to buy a Hewlett-Packard ACVM. The vacuum tube version was the model 400D and the solid-state version was the 400E. They also had the 3400A true rms ACVM. Heathkit also made an ACVM kit. All of those models are considered to be antiques, but they are still excellent performers and will be less expensive and out-perform the new Asian imports by significant amounts.


    DVM or Differential Voltmeter

    The differential voltmeter is primarily a Fluke instrument, although there were some made by companies such as Kintel and Cohu, brands that have since disappeared from the marketplace. The differential voltmeter was the predecessor of the DMM with its ability to make very accurate
    measurements of dc voltage, and later, ac voltage. The DVM worked by comparing the voltage to be measured against an internal, very accurate, voltage standard. The technician twirled a series of switches, each representing one of ten digits of a decimal place until an analog meter on
    the front panel indicated a "balance", whereupon the dial reading and the voltage being measured were the same. Accuracy for the run-of-the-mill DVM was at least ±0.1% and many models were better than ±0.05%.

    In their heyday, the DVM was king of the hill for accuracy there was nothing better, short of a trip to a standards lab. But these days? No, the DMM is just as good, and new, lab-grade DMMs run circles around the DVM both in accuracy, speed and ease of use. But even today, the DVM has one feature that has yet to be equaled in any voltage measurement instrument. At balance (when the dial voltage equals the measured voltage), the input resistance of a DVM is INFINITE! It doesn't load the circuit being measured in the least bit! There are some lab-grade
    DMMs that have input resistances of 100M ohms and 1000M ohms, which for all practical purposes, is almost no load to the circuit at all. But considering that a meter like that will sell for $5000 and you can get a working DVM off ebay for $50 .... well, you figure it out.



    RF Voltmeters or RF Millivoltmeter

    These instruments are more often called millivoltmeters, because they aren't designed to measure much over 10 volts maximum. An RF millivoltmeter is capable of measuring ac voltages up through 1 GHz and usually come with special accessory kits to help achieve those high-
    frequency measurements. They are frequently used to check the flatness of signal generators over their entire frequency range. RF millivoltmeters are able to measure such high frequencies because they use a solid-state rectifier right in the probe head. But because of this, they are also very susceptible to high ac voltages or dc voltages, either of which could burn out the rectifier. Often, these meters have correction tables for the higher frequencies.

    Millivac was a big name in RF millivoltmeters. Hewlett-Packard also made the model 411A RF Voltmeter. Be very careful buying these from surplus outfits or from on-line auctions. It's very likely that the diodes in the probe are blown and it will be either impossible or very expensive
    to replace them. Besides, do you really need one? If you have a calibration lab and/or work on lab-grade signal generators, then one of these may be for you. RF voltmeters often came with or had an option for a kit of special adaptors for specialized measurements. These connector kits often cost as much as the basic meter. These days, it's difficult to find accessory kits that are complete with all the parts.


    Other Specialized Meters

    There are other meters designed for specialized measurements, usually being limited to only one function, but several ranges. The most common that you'll see is the typical digital capacitance meter. There are also milliohmmeters, which are special ohmmeters designed for measuring very small resistances. These meters use "four-terminal" or "Kelvin" measurement techniques to eliminate the contact and lead resistances of the probes.

    Capacitance, inductance and resistance used to be commonly measured on "bridges". Knight-Kit, Heathkit and EICO made kits that were resistance and capacitance bridges. In their day, it was the only easy way to measure capacitance. These days, a DMM and a digital
    capacitance meter will run circles around the bridges. Other companies, including Heathkit and Hewlett-Packard, have made RLC bridges for measuring resistance, inductance and capacitance. These are usually very specialized instruments and unless you work in designing or homebrewing communications gear, you probably won't have much use for them.

    Dean
     
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  6. windozeuser

    windozeuser New Member

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    wow thanks everyone.

    Thanks Dean for the Good Article!
     
  7. ljcox

    ljcox Well-Known Member

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    Analogue meters are less likely to suffer interference from the system being measured. I have heard of digital meters giving strange results which did not occur when an analogue meter was used.

    Peak Electronic Design in the UK sell a nice range of test gear. see www.peakelec.co.uk

    Len
     
  8. Dean Huster

    Dean Huster Well-Known Member

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    That' something I've been needing to add to that article. If a power supply has a horribly noisy, unbypassed line, it can cause a digital meter to totally buggy. Another problem is using the meter near a transmitter when it can exhibit the same flakey symptoms.

    And another problem with an analog meter is using around strong magnetic fields.

    Dean
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    That 'can' be an advantage 8)

    The line output transistor in a TV set is usually fed from something like 135V, but because it's switched ON and OFF, and feeds a tuned transformer, the result is a large pulse on the collector (about 1000V or so).

    If you measure the collector voltage with a digital meter, it reads 135V, BUT all the decimal points on the display light up!. This happens on all the digital meters I've ever tried, so you not only get the voltage reading you wanted, but you also know the stage is running.

    An analogue meter will just read 135V, with no sreange effects.

    Yes, they are PIC based, the company is only about 30 miles away from where I live.
     
  10. chemelec

    chemelec Well-Known Member

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    I find Analogue Meters Much Better whan measuring Varying Signal levels.

    Such as the output of an Audio Amplifier.
    Or a Varying DC Collector voltage on a Transistor as a signal is applied.

    Because there are no Update times on an analogue meter it appears to make more sense to me.

    However I Do realize that the Analogue is also not a Precise Reading, because the Needle Can't Physically Move fast Enough to give a True Reading.

    And Yes an Oscilloscope is Much better for this, but not always as available for everyone.

    I also Find a Digital, LED Display, Much Better around VERY HIGH VOLTAGES. Rather than LCD Displays. Extreme Electrostatic Fields can really screw up LCD's.

    Just my opinion.
    Gary
     
  11. ThermalRunaway

    ThermalRunaway New Member

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    I'm told that an analog meter is also better for measuring leakage in components such as diodes, because they load the component much more than a digital meter. I've always used a digital meter myself.

    Brian
     
  12. mtaylor

    mtaylor New Member

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    I've found that even the cheapest most basic analogue voltmeters can measure the voltage of a synthetic sinewave (e.g. the output from a PWM Inverter) while a Digital meter will give you rubbish unless you go for one with a special function for this (e.g. "True RMS").

    Hope this helps!
     
  13. electronist

    electronist New Member

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    I guess you can use analog multimeters for a quick check of capacitors. The flicker of the needle indicates the state of the capacitor
     
  14. Dean Huster

    Dean Huster Well-Known Member

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    "However I Do realize that the Analogue is also not a Precise Reading, because the Needle Can't Physically Move fast Enough to give a True Reading."

    Considering that most DMMs have a sample/update cycle that often is no faster than 2 or 4 readings per second, such a DMM would not follow the voltage as quickly as an analog meter. Even if the meter updates at 1000 samples per second, you have to have a brain that is infinitely superior to mine (most are anyway!) to see, interpret and follow those digital updates vs. simply watching the swing of an analog meter needle.


    "I've found that even the cheapest most basic analogue voltmeters can measure the voltage of a synthetic sinewave (e.g. the output from a PWM Inverter) while a Digital meter will give you rubbish unless you go for one with a special function for this (e.g. "True RMS"). "

    The bulk of DMMs and analog meters measure the AVERAGE value of an ac waveform and display this measurement in RMS units. It's simple technology with the problem that only a sine wave will be measured correctly. That is the ONLY reason for "true RMS" meters. They will display the true RMS voltage regardless of the waveshape. To say that a digital meter will "give you rubbish" doesn't make a lot of sense. A non-true-RMS meter, regardless of whether is is analog or digital, will give you an erroneous reading of a synthetic sine wave IF the manufactured waveform is a lousy replica of a sine wave.

    Now, I would expect the DMM, even if true-RMS, to be problematic in this situation, but only because possible transition spikes that could feed through the circuitry and goof up the electronics and make the display go bonkers.

    Dean
     
  15. Blue Dog

    Blue Dog New Member

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    I still use an old Simpson to read the serial data on fuel injected Ford engines (slow enough rate you cab count the needle sweeps and determine the trouble code).
     
  16. RODALCO

    RODALCO Well-Known Member

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    Give me an analogue meter anytime !

    As already said they are perfect to follow fluctuating voltages or currents. Also they impose a burden upon the circuit measured. (20kOhm/volt)
    Try to measure across a open mains switch, you usually pick up a voltage 60 or so volts on a DMM because of its very high impedance (1Megohm+).

    For insulation testers they are great too. I use a Kyoritsu 3132 for the latter. perfect to see a capacitor charge up in a circuit.

    Best of all, they don't require batteries for current or voltage measurement

    Ok, for most quick measurements i use a DMM too. they have advantages too, easy to read and very accurate.
     
  17. mdanh2002

    mdanh2002 Member

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    Theoretically this is right, when measuring current or voltage the analog multimeter can use the power from the input to make the needle move. But my analog multimeter needs 1 big 9V battery (which runs out very fast) and it doesn't work at all when I remove the battery (even when switched to voltage/current mode)

    And maybe using the power from the input for the measurement circuit in voltage/current mode affects the accuracy?
     
  18. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    That's because it's an active meter, not a normal passive analogue one.

    Yes it does, but so does a DMM as well - in fact, on high voltage ranges a DMM has a greater effect than a standard analogue meter.
     
  19. Sceadwian

    Sceadwian Banned

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    The battery is to power the opamps that buffer the input voltages. Otherwise the voltages produced themselves drive the analog meters. This in modern high impedance circuits would require very low impedance sources to achieve linearity and accuracy.
     
    Last edited: May 19, 2007
  20. Dawny

    Dawny Member

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    Call me silly but I like analogue meter's because they look better in sound based circuits.
     
  21. Leftyretro

    Leftyretro New Member

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    Well I 'grew up' using analog meters, still have a Simpson stored away somewhere :confused: . Great dependable and deserves it's rep.....

    However once I got the chance to use a Fluke DMM at work decades ago I find I haven't used a analog meter in a very long time. At home now I use a Fluke model 87 true rms DMM when I need portablity and a love of my life (I'm such a nerd!) is a bench model Fluke 45 DMM. The 45 is so much fun to use, when I get bored I search old old batteries to measure and decide to keep or dispose :p

    Lefty
     

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