I was thinking to use a resistor in series with the meter and pulse the voltage to get the 4 to 20ish.
I started out with 0.5Hz 50% just to get things setup
181A read 20.017/4.002
869s read 20.022/4.002
At 50Hz, 500uS pulse
181A reads 20.11
869s reads 20.9
50uS pulse
181A reads 20.13
869s reads 9.4 ***
20uS pulse
181A reads 17.74869s reads 8.5
Now the funny one is the Extech which was really good in voltage mode. In current mode even with a 5mS pulse, it could not detect it. Went back to repeat the voltage test with the Extech and realized I had forgot how to use the peak mode. I then tried the peak detect in current mode and it worked.
It also turns out the 181A needs a fair amount of time to settle. Several seconds (5 or more) The Brymen on the other is correct.
Here is the new data for the Extech and the UNI-T.
50uS EX540 19.86mA, UT181A 20.13mA
20uS EX540 19.86mA, UT181A 20.16mA
10uS EX540 19.85mA, UT181A 20.13mA
5uS EX540 19.80mA, UT181A 20.17mA
2uS EX540 18.68mA, UT181A 15.97mA
1uS EX540 15.43mA, UT181A 10.94mA
Thinking back, what was the fastest 4-20 I ever worked on.....