User manual

Let’s now say you need to do the same thing on a modern circuit or chip with say a 1.2V power
supply. That same 200mV burden voltage is now a whopping 17% (200mV / 1.2V * 100) of the supply
voltage. Your circuit will likely fail to function correctly and this is clearly not acceptable, not to
mention inaccurate.
Think this is only a problem with “cheap” meters? Think again. The Fluke 87-V, probably the most
popular high-performance meter available has a burden voltage of 1.8mV/mA (which is still pretty
good). So the above numbers are even worse – a 360mV drop for a 200mA current.
Sure, you can switch up a current range, using the 10A jack, with its burden voltage of say 10mV/A,
giving you a very nice drop of only 2mV. But your display is now showing 0.200 or 0.20 instead of
200.0 – you’ve just lost a valuable digit or two of resolution. And the higher 10A current range is likely
much less accurate than the mA range too!
Let’s have a look at the quoted burden voltage of some typical multimeters:
Multimeter Model Approx
Cost($)
Burden
Voltage
(mA range)
Burden
Voltage
(µA range)
Meterman 5XP (3.5 digit) $65 1V max 300mV max
JayTech QM-1340 (4.5 digit) $99 5mV/mA 0.11mV / µA
Meterman 30XR $120 4.6mV / Ma 1mV / µA
Protek 506 $175 1mV / mA 1mV / µA
Meterman 37XR (10,000 count) $250 10mV / mA 1mV / µA
B&K 390A (4000 count) $380 2V max 500mV max
Fluke 77 series III (3.5 digit) $400 6 mV / mA N/A
Fluke 77 series IV (6000 count) $425 2mV / mA N/A
Fluke 79 series III (3.5 digit) $375 11mV / mA N/A
Fluke 177/179 series IV (6000 count) $430 2mV / mA N/A
Fluke 27 $900 5.6mV / mA 0.5mV / µA
Fluke 80 series V (4.5 digit) $720 1.8mV / mA 0.1mV / µA
Agilent U1251A (4.5 digit) $680 1mV / mA 0.1mV / µA
Extech MM570 (500,000 count) $680 3.3mV / mA 0.15mV / µA
Fluke 289 (50,000 count) $950 1.8mV / mA 0.1mV / µA
Gossen MetraHit E-XTRA (60,000
count)
$1700 300mV max 150mV max
Fluke 8808A (5.5 digit) $1100 1mV / mA 1mV max
Fluke 8846A (6.5 digit) $2100 500mV max 15mV max
Keithley 197A Microvolt (5.5 digit) N/A 300mV max 300mV max
As you can see from the table, things can improve a bit with the more expensive meters, particularly
on the µA ranges. But an expensive precision meter is by no means a guarantee of a low burden
voltage. Even many very expensive top-of-the-line bench meters can have unacceptable burden
voltages for many applications.
It should be noted that whilst some meters will have a fixed burden voltage for all mA ranges, others
like the Meterman 30XR have individual specs for each range – in this case: 2mA range =
100mV/mA, 20mA = 13mV/mA, and 200mA = 4.6mV/mA
Some popular and highly regarded meters like the Meterman 37XR and Fluke 79 are particularly bad
on their mA range, an order of magnitude worse than some cheaper meters – beware.