A D(u)MM question  - Page 1
Forum section: electronics / testgear

author: McJim56
author_rank: Newbie
timestamp: November 04, 2023, 01:50:27 am
content: Hi all, and new to the forum shout out to Dave!!I’ve just found here the Tekronix DMM 4020 and Fluke 8808a are one in the same.I’ve already (by mistake) purchased Agilent 34401a. It’s a quiet good instrument but doesn’t do exactly what I want. I was looking for dB to watt function.David @ ElPaso Tube Amps uses his Tek math function to select 2,4,8 ohm across the dummy load for output in watts.I suppose my question is am I limited to these two models for what I’m trying to accomplish?Trying to avoid another $300+ mistake.Thanks in advanceJim

author: coromonadalix
author_rank: Super Contributor
timestamp: November 04, 2023, 03:15:48 am
content: well find a meter who can do that for you and or associated software if they are or have themnormally you buy a wattmeter ... who's in a sense not a multimeterwith an multimeter you read voltage created on power resistors leads ...you use a signal generator at given frequencies and amplitudes and read the amplifier output on the load(s)and many websites offer the db to watts calculations ??

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2023, 03:46:33 am
content: Quote from: McJim56 on November 04, 2023, 01:50:27 amCould you explain in detail (step-by-step) how that is managed?Edit: I found it in the manual. Never knew it had that feature! You can select a secondary display as well, such as ACV or FREQd.

author: bdunham7
author_rank: Super Contributor
timestamp: November 04, 2023, 04:22:46 am
content: To answer your actual question, I'm not aware of any other meters with a power function that works this way.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 04, 2023, 07:38:38 am
content: With a programmable math function other meters should be able to provide such an output. It is still relatively easy to do the math separate and use the voltage reading.

author: 2N3055
author_rank: Super Contributor
timestamp: November 04, 2023, 08:07:30 am
content: Quote from: bdunham7 on November 04, 2023, 04:22:46 amI know for sure that old Fluke Scopemeter 97 had that function in meter mode. There must have been more meters out there that had that function.My Metrix MTX3293 has the function, for instance. You enter load resistance and it calculates power from voltage.And yes any meter with math can do it. But it needs to have more math than Ax+B.. You need to calclulate U2/R

author: McJim56
author_rank: Newbie
timestamp: November 04, 2023, 12:26:54 pm
content: @bdunham7 thanks for looking 👀Yes a nice LDR readout to see from a distance. No calculator, too much trouble.Jim

author: AVGresponding
author_rank: Super Contributor
timestamp: November 05, 2023, 09:19:27 am
content: This any help?

author: Kean
author_rank: Unknown
timestamp: November 05, 2023, 09:59:08 am
content: The Agilent 34401A can do a dBm power calculation, but it is limited to 17 fixed resistance values from 50 to 8000 ohms.It doesn't have an option for displaying Watts, and that does seem to be an uncommon feature on DMMs even if it is a pretty simple calculation.

author: alm
author_rank: Super Contributor
timestamp: November 05, 2023, 10:57:29 am
content: A different reference resistor is just an offset in dB value. Can you apply that for the 34401A? Possibly by connecting a 0 dB signal and zeroing it? TheKeithley 175 manualdescribes that procedure on page 2-8.

author: RoGeorge
author_rank: Super Contributor
timestamp: November 05, 2023, 11:20:11 am
content: mtx3283, too, can display dBm and W for an R value of your choice between 1-10000 ohms.

author: electr_peter
author_rank: Unknown
timestamp: November 05, 2023, 04:44:35 pm
content: Agilent/Keysight U1272A handheld DMM also hasdBm(reference 1-9999 Ohm) ordBV(reference 1V) display option.

author: bdunham7
author_rank: Super Contributor
timestamp: November 05, 2023, 05:32:07 pm
content: Quote from: alm on November 05, 2023, 10:57:29 amYes, very easily. If you just apply 2.828VAC and press SHIFT then NULL(dB) the 34401A will then read dBW/8R, or 0dB for 1W with 8R impedance and so on. But I think the OP was looking for watts displayed directly and that is a pretty niche feature.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 05, 2023, 11:33:55 pm
content: Escort 97 will display in dBm, Voltcraft GDM705 in dB but neither has a Watts option.