Aim-TTi 1908 5 1/2 Digit Benchtop Multimeter (preview)

[kish]

I was looking for a benchtop multimeter and I decided to buy the Aim-TTi 1908 5 1/2 digit bench multimeter (datasheet) from Saelig.
I like the 1908 for its big, easy-to-read display. There's a dedicated physical button for each measurement type, without the need to press/hold shift buttons, or fuss with menu system.
I think the most important part about a DMM is that it has to be clean and easy to use! Also: no fans! Completely silent.

Designed & Made in England!

(these images are clickable for full resolution)


My current go-to multimeter is the Fluke 87V, and while it's a great portable DMM, it has its downsides for me in a benchtop application.
Primarily, while taking measurements on the bench, it's difficult to make readings while its laying flat on the bench. Propping it up is also annoying at times because the unit is tall, and has a tendency to fall over. My biggest issue is the backlight-- it keeps turning off and its annoying to keep pressing it to keep it awake.

I considered several other DMM's in the 5 1/2 - 6 1/2 digit range. Unfortunately, all of them do have audible fan(s):
1. Rigol DM3058E - 5 1/2 digit - (the display is too small, hard to read measurements)
2. SIGLENT SDM3055 - 5 1/2 digit - (great display, but slow sampling rate according to reviews)
3. Keysight 34461A - 6 1/2 digit - (probably the best pick, but overkill for my uses. My 2nd pick)
4. Fluke 8845A - 6 1/2 digit - (probably a very accurate DMM, but that display is terrible)

There isn't too many reviews of the Aim-TTi 1908 on the internet (save for a single lonely review on Amazon). So first, some exterior views:

(front)


(front 3/4 view)


(top view)


(rear view)
(Mine comes without the LAN/RS 232/GPIO interface. If you want those, you can get the slightly upgraded version, 1908P for a bit more.)


(bottom view, fuse compartment)


(easily accessible fuse holders)


(display and buttons)


(input terminals)


I'll start with the coolest/unique feature of Aim-TTi 1908:

(what's with this "charging" light...?)


(that's right, it has a built-in Ni-MH battery for mains-free portable usage!)


Probably the biggest downside about the 1908 is that, while it's a supposed 5 1/2 digit meter, it's only 120,000 counts! That means that 5 digits of precision at 11.9999V becomes 4 digits of precision at 12.000V.

For example, the ranges are as follows:
1V range
min- 0.12000
max- 1.19999

10V (e.g. measuring 1.5V batt)
min- 01.2000
max- 11.9999

100V range (e.g. measuring 12V batt)
min- 012.000
max- 119.999

1000V (e.g. measuring 120V AC mains)
min- 0120.00
max- 1119.99

So I personally don't know how to classiy this DMM. Precision-wise, I guess it's somewhere between a 4 1/2 digit and 5 1/2 digit DMM? In my opinion, it's misleading from Aim-TTi to market this as a "5 1/2 digit" DMM.
For example, it's closest rival, SIGLENT SDM3055 is also a 5 1/2 digit DMM, but it has 240,000 counts, so it's a "true" 5 1/2 digit DMM. As I understand, a DMM needs to have at least 200,000 counts to be considered "5 1/2 digit". (0 or 1, followed by 5 digits of precision at all times)

Here are some measurements I took in comparison with my Fluke 87V. I'm no Dave Jones with high precision calibrated equipment, but I try my best! By the way, the Fluke 87V is a 6000 count DMM. However, in high-resolution mode it can do up to 60,000 counts, I think. Thus, I gues the Aim-TTI is only 2x better at 120k counts?

120V mains measurement:

(Fluke in normal mode)


(Fluke in high-res mode)



1.19999V to 1.2000V range crossover point:



11.9999V to 12.000V range crossover point:



And lastly, I will mention it has several "dual measurement" modes. Here it is measuring DC voltage, and the AC component of DC voltage:


I just got the unit so I'll need to read the manual and play around with it a bit more. There's a ton more technical info in the datasheet for those interested.
Overall, I think it's a good unit for my hobbyist needs, and for anyone who can live with it's precision limitations. It's an an easy-to-use benchtop DMM, completely silent, and portable. It does have a very simple display, but that's also the beauty of it-- no fuss. I'd take function over form any day.
If anyone wants me to testing anything specific, please let me know.

[BravoV]

If anyone wants me to testing anything specific, please let me know.

Tear down photos maybe ?

[kish]

Yes, I was afraid of that. Unfortunately that's the one thing I cannot do 
This unit comes with a 3-year warranty from Aim-TTi. With the fuse compartment accessible from the outside, there's no good reason for an end-user to be poking on the inside.
I also don't want to mess with the calibration by opening it (if that's a thing).

[garrettm]

Probably the biggest downside about the 1908 is that, while it's a supposed 5 1/2 digit meter, it's only 120,000 counts! That means that 5 digits of precision at 11.9999V becomes 4 digits of precision at 12.000V.

You need to be careful when you talk about precision. What you are really referring to is resolution, i.e. number of decimal digits. Precision is a metric that relates to the stability of the meter over time. The dart board analogy is often quite elucidating: You can be accurate, have darts hit a certain ring, but not be precise, darts are dispersed loosely all around the ring. You can be precise, darts closely clustered together, but also not very accurate, darts are far away from the bullseye.

Unfortunately, programmers have used the word "precision" to imply the number of valid decimal digits stored in a floating point number and conflicts with terms used in metrology and sciences that involve physical measurements.

To be honest 120000 counts is expected. Thats 100,000 counts with 20% overranging. Only a few instruments do 100% overrange (2,000,000 etc.) and even fewer that do 300,000 or 3,000,000 counts. So nothing unusual here. The "5.5 digits" on the front panel says it all: The most significant digit is limited, hence the 0.5 in 5.5.

[J-R]

Very nice preview, links and high quality photos.


When shopping I also find the "digits" rating misleading and overly abused and hunt for the counts in the specs.

But even the specs can be tricky to translate to the real world.

For example, the Fluke 87V is sold as 6,000 counts normally and 20,000 counts in hi-res mode.
In reality it can display 6600 so I consider it 6,600 count.
It cannot display 20000, only 19999 so I consider it 19,999 count in hi-res mode. 
Counting up it switches at 6601 and going down it switches at 539.

The "120..." count "issue" exists elsewhere.  The 34401A is 1,200,000 counts, rated as 6.5 digit.

[kish]

Thanks! Yeah, some manufacturers are better at clearly disclosing the counts than others.

For example, in Siglent's line up, they're up front and clear about their counts, right up in the header banner.

On the other hand, Keysight is terrible at disclosing the counts. Nowhere on their product page for the 34461A do they mention counts. Not even in their datasheet. Are we supposed to assume that 6 1/2 digits automatically guarantees at least 2,000,000 counts?
Only on their entry level 5 1/2 digit DMM, Keysight U3400, do they mention the counts (120k). It's almost as if disclosing counts is only for cheaper DMMs.

To Aim-TTi's credit, they're quite upfront about their DMM being 120k counts, so I knew exactly what I was getting. If I had bought it expecting 200k, it would be a different story.

> The "120..." count "issue" exists elsewhere.  The 34401A is 1,200,000 counts, rated as 6.5 digit.

That is interesting! How do you know this? Their datasheet doesn't even mention the 1.2 mil counts.

[kish]

Probably the biggest downside about the 1908 is that, while it's a supposed 5 1/2 digit meter, it's only 120,000 counts! That means that 5 digits of precision at 11.9999V becomes 4 digits of precision at 12.000V.

You need to be careful when you talk about precision. What you are really referring to is resolution, i.e. number of decimal digits. Precision is a metric that relates to the stability of the meter over time. The dart board analogy is often quite elucidating: You can be accurate, have darts hit a certain ring, but not be precise, darts are dispersed loosely all around the ring. You can be precise, darts closely clustered together, but also not very accurate, darts are far away from the bullseye.

Unfortunately, programmers have used the word "precision" to imply the number of valid decimal digits stored in a floating point number and conflicts with terms used in metrology and sciences that involve physical measurements.

To be honest 120000 counts is expected. Thats 100,000 counts with 20% overranging. Only a few instruments do 100% overrange (2,000,000 etc.) and even fewer that do 300,000 or 3,000,000 counts. So nothing unusual here. The "5.5 digits" on the front panel says it all: The most significant digit is limited, hence the 0.5 in 5.5.

Yes, I'm coming from a programming background, so it's only natural for me more digits = more precision .

So to summarize your point, in regards to DMM's:
Accuracy = how close the reading is to the actual value
Resolution = precision (in general terms) = improves confidence in accuracy
Precision = how accurate the DMM's readings are over time (as internal electronics ages).

[coromonadalix]

I love Siglent with their "Real" digits  loll

[J-R]

> The "120..." count "issue" exists elsewhere.  The 34401A is 1,200,000 counts, rated as 6.5 digit.

That is interesting! How do you know this? Their datasheet doesn't even mention the 1.2 mil counts.

I tested mine and that is the maximum it can display, at least in DCV.

[coromonadalix]

For the 34401a   this web site give you more  specs ....
https://www.atecorp.com/products/keysight-technologies/34401a

Lots of makers  plays with the displayed digits vs resolution vs accuracy  ....    we love big numbers  loll


The only 3,030,000 counts dmm i know are the keithley 196 and its Tektronix dm5120 brother
And  Gossen Metrawatt 28 and 29s are 310,000 counts, 5 3/4 digits in a few modes and 4 3/4 digits in other modes  ...

Precision or Accuracy is another thing  loll

[J-R]

The basic accuracy ratings are also abused as I found when comparing the U1282A and the U1461A.  Sometimes you will see a very desirable percentage but with a large number of +/- digits and on the flip side a very poor percentage with very low +/- digits.

Real world accuracy is also a factor as most of us would not accept a DMM that only just met it's published accuracy.  For example if the U1282A were consistently say 8 counts out it would still be in spec but that would be terrible.

[coromonadalix]

Same for the many brymen / clones  at 50,000 count and   oh    the 500,000 count mode     loll   

The high resolution vs the low / normal resolution .... they say,    we had some war of words for that in past threads  loll



Anyway  the OP TTI meter  seems very nice   clean and simple to use      if he have'nt paid a fortune   that's good enough  for me

Sure a teardown would be nice  loll  and see what is the reference used ??

[J-R]

Same for the many brymen / clones  at 50,000 count and   oh    the 500,000 count mode     loll   

The high resolution vs the low / normal resolution .... they say,    we had some war of words for that in past threads  loll

Yes, that is perhaps a bit gimmicky...but also can be useful for certain purposes.

As received my BM869s was frequently 100+ counts out in 500,000 count mode.  After a quick calibration it is now never more than 15 and typically only 1-5.

This does bring up the point that having digits on your DMM that can be trusted is as important as having the digits at all...

[coromonadalix]

Same for the many brymen / clones  at 50,000 count and   oh    the 500,000 count mode     loll   

The high resolution vs the low / normal resolution .... they say,    we had some war of words for that in past threads  loll

Yes, that is perhaps a bit gimmicky...but also can be useful for certain purposes.

As received my BM869s was frequently 100+ counts out in 500,000 count mode.  After a quick calibration it is now never more than 15 and typically only 1-5.

This does bring up the point that having digits on your DMM that can be trusted is as important as having the digits at all...

+1   

But  the problems are to know when you can count on them,   calibration is important, but sometimes its hard to justify it's pricing, luckily on some brand(s) you can make it yourself

My flukes 189 cost 75$ cad to calibrate,  my 34401a  is 150$ cad        and i'm not equiped with any references (resistors, ac or dc sources) 

The only precisions stuff i have, are some Fluke 343 left over  boards with 0.035% resistors on them. 

[garrettm]

So to summarize your point, in regards to DMM's:
Accuracy = how close the reading is to the actual value
Resolution = precision (in general terms) = improves confidence in accuracy
Precision = how accurate the DMM's readings are over time (as internal electronics ages).

Pretty close.

Accuracy really represents the error bounds that the measurement is inside of. The meter could be spot on, or anywhere inside the bounds. But hopefully not on the edge, as that would imply a marginal meter.

Resolution is the smallest value measureable in a given range. For instance, 100 nanovolts on the 100 mV range. But this implies number of digits, and this is how most people interpret resolution.

Precision generally is interpreted as long term drift measured in PPM / year. It relates to how well a meter holds its calibration. A low precision instrument will drift more rapidly and need frequent adjustment to stay within its accuracy bounds. A precision instrument will hold its calibration for many years, rarely needing any adjustment at all.

Calibration in general is not about adjusting an instrument. It is about creating a historical record of a meter's measurements vs primary standards. This then tells you the precision of the instrument and lets you know when the meter went outside its error bounds, at which point that range would need adjustment.

It's a lot of jargon to take in, but hopefully that helps make sense of it all.

[BravoV]

So to summarize your point, in regards to DMM's:
Accuracy = how close the reading is to the actual value
Resolution = precision (in general terms) = improves confidence in accuracy
Precision = how accurate the DMM's readings are over time (as internal electronics ages).

A pic speaks thousands words ...

[evava]

My current go-to multimeter is the Fluke 87V, and while it's a great portable DMM, it has its downsides for me in a benchtop application.
...
My biggest issue is the backlight-- it keeps turning off and its annoying to keep pressing it to keep it awake.

the Fluke 87V has no backlight timer. Once turned on, it only turns off when the button is pressed again, or if the meter automatically powers off after 30 minutes. If the auto power off is disabled and the backlight is activated, both the meter and the backlight will stay on until the battery is depleted.

(taken from other thread on this forum)

[Fungus]

Same for the many brymen / clones  at 50,000 count and   oh    the 500,000 count mode     loll 

Yes, that is perhaps a bit gimmicky...but also can be useful for certain purposes.

As received my BM869s was frequently 100+ counts out in 500,000 count mode.  After a quick calibration it is now never more than 15 and typically only 1-5.

At what temperature? Temperature starts to play a big role with that many digits.  Raise it a degree and you might have 100 digits.

No non-temperature-controlled meter is ever going to be 5 1/2 digits accurate but the digits are useful for seeing very small changes over time.

[kish]

One complaint that the Amazon reviewer had about this DMM is its high standby power, due to it constantly trickle charging its internal Ni-MH battery.
With the rear (main) power switch on, and the front power switch off (standby mode), the unit draws 2.4W. A standby power of 2.4W, is that good or bad?



This is with a fully charged battery (front panel orange "charging" light is off). So, I don't think it's charging the battery at all. It would be poor design to constantly charge/keep the Ni-MH battery at 100%.

According to the owner's manual:

4.3 AC Power and Battery Operation

The instrument can be operated from AC power or from internal batteries which are recharged as required when AC power is connected. A red LED is illuminated whenever AC power is connected and a yellow LED is illuminated whilst charging is taking place.

Battery Life from fully charged is approximately 20 hours with the backlight on, and up to 40 hours with the backlight off. Under battery operation, a battery symbol will appear on the display if the charge level falls below about 10%. The approximate charge level can be checked from the Utilities menu.

Perhaps it's keeping some other circuits alive/"warmed up" for accurate measurements. When the unit is powered on (out of standby mode), it draws 3W from the wall.
Regardless, it might be a good idea to put the meter on a bench power strip, and keep it turned off (if it won't be used for while), to avoid any standby power usage.

[kish]

It's interesting, in the owner's manual, it states that the scale length (aka resolution) is 5 1/4 digits (120,000 counts). So why not market this as a 5 1/4 digit DMM? Or is that not a thing?

[garrettm]

It's interesting, in the owner's manual, it states that the scale length (aka resolution) is 5 1/4 digits (120,000 counts). So why not market this as a 5 1/4 digit DMM? Or is that not a thing?

That looks like a typo. It’s not uncommon to see errors in manuals or other product literature (I find them all the time).

You can have different "fractional digits" for the MSD, but these are always larger than 1/2, not less. Nearly all manufacturers use 1/2 to imply the MSD is limited to 0 or 1 (or whatever the max value of the MSD is)--even if they could legitimately use a larger fractional digit to denote the MSD.

I wouldn't pay too much mind to fractional digit notation, it's ultimately a pointless marketing gimmick. The more tactful approach is to state the FS counts to show that the MSD can go higher than 1. This is how HP marketed the 3457A DMM: 6.5 digits with 3,000,000 counts FS. Clear and simple.

[JohnG]

So to summarize your point, in regards to DMM's:
Accuracy = how close the reading is to the actual value
Resolution = precision (in general terms) = improves confidence in accuracy
Precision = how accurate the DMM's readings are over time (as internal electronics ages).

A pic speaks thousands words ...

I have never in all my life seen this definition for precision. What they call precision looks like noise to me or drift to me, depending on the applicable time scale.

Cheers,
John

[nfmax]

The ISO/IEC International vocabulary of metrology ISO Guide 99:2007 defines it thus:

2.15
measurement precision
precision
closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions
NOTE 1 Measurement precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation under the specified conditions of measurement.
NOTE 2 The ‘specified conditions’ can be, for example, repeatability conditions of measurement, intermediate precision conditions of measurement, or reproducibility conditions of measurement (see ISO 5725-3:1994).
NOTE3 Measurement precision is used to define measurement repeatability, intermediate measurement precision, and measurement reproducibility.
NOTE 4 Sometimes “measurement precision” is erroneously used to mean measurement accuracy.

[JohnG]

The ISO/IEC International vocabulary of metrology ISO Guide 99:2007 defines it thus:

2.15
measurement precision
precision
closeness of agreement between indications or measured quantity values obtained by replicate measurements on the same or similar objects under specified conditions
NOTE 1 Measurement precision is usually expressed numerically by measures of imprecision, such as standard deviation, variance, or coefficient of variation under the specified conditions of measurement.
NOTE 2 The ‘specified conditions’ can be, for example, repeatability conditions of measurement, intermediate precision conditions of measurement, or reproducibility conditions of measurement (see ISO 5725-3:1994).
NOTE3 Measurement precision is used to define measurement repeatability, intermediate measurement precision, and measurement reproducibility.
NOTE 4 Sometimes “measurement precision” is erroneously used to mean measurement accuracy.

Wow, learn something new every day.

I find the term "gauge reliability and repeatability" or gauge R&R to be more meaningful. The ISO standard definition is fairly vague, or, if you prefer, rather imprecise  .

Cheers,
John

[Fungus]

I have never in all my life seen this definition for precision.

And I've never seen the term "resolution" applied to a multimeter.

Precision: Number of digits (or "counts" in the multimeter world - it might not have a range that's a perfectly round decimal number)

Accuracy: How close those digits are to reality, often expressed as a percentage of reading and number of counts.

eg. My Brymen in CD mode has 500,000 counts and 0.02%, 2 counts accuracy.

Note that 0.02% of 500,000 is 100 counts so the meter isn't claiming that all those digits are accurate.

(although in practice they're usually very close to those 2 counts...that's digital calibration for you!)