Hello mates,
does anyone knows a multimeter which you can input a equation to be solved?
Let's say i'm tapping a 4-20mA loop from a temp sensor and I want to see the temperature from the sender, not the current...
So, is there something like a programmable multimeter? I never played with those fancy fluke connect but I do not recall this functionalist.
for a 4-20mA transmitter (your temp sensor), a large part of it will come down to if its linear in reading or not,
For actual multi meters you likely wont find anything under $400 with this kind of feature, but you may find 4-20mA displays that allow for custom scale offset and units.
For a budget meter, if you can get something with a serial connection of some kind, you can have software on external device to do it fairly easily. As a standalone, programmable meters certainly exist, but as mentioned, they're not cheap (and are usually bench meters).
Could you use a BJT to increase to something resembling the reading? not good for power consumption, but a little analog math could be an interesting hack for it.
Some bench meters can do a limited amount of math. For example, see attachment for the math features of a Prema 6031A meter. The Keithley 200x series can do a simple linear equation mx+b, as can some HP meters. There were even some meters old (Solartron?) meters that were branded "computing multimeters". Some could run small programs. These days a more common solution on the bench would be to do the math on a computer that is hooked up to the meter. Not sure about any handheld options.
The Rigol DM3058/3068 has a function they call "User-defined sensor" where it can convert any of the measurable quantities (voltage, current, resistance) into a display reading with a unit of choise. You do this by inputting datapairs into a list forming a curve (your basic list can be two entries forming a straight line). There's a supporting software (Rigol Ultra Sensor) which apparently allows you to manage this function easier than using the thru the front panel - I haven't tried either method in my DM3068.
I seem to remember something regarding a potential issue using this function but I can't remember the details - if it was on the 3058 only and only when configuring using the software and/or SCPI but I don't know. Some searching on the forum should dig it up.
An old piece of kit that could do this is the Wavetek Model 52 Datamultimeter. They show up occasionally on eBay. But they would be 30 years old and only have 4.5 digit resolution in the measurement. It has "Math" channels that can take DMM data and apply formulas. Another thing I designed oh so many years ago. I've had a hankering to do an updated version.
Assuming you are in the field with the 4-20 and want something portable. Some of the meters do offer Bluetooth so it would not be too difficult to write an interface for your cell phone that has all your conversions built into it.
Or IMO, the ultimate would be use a tablet PC and run LabVIEW.
Is there a proper version of LabVIEW for tablets? I know they have the dashboard thing which is just a remote interface to LabVIEW running somewhere else. I guess you could run LabVIEW on a tablet that runs a full Windows version with x86 processor, but I doubt the controls will be very nice to use. If all you need is graphing / readout then I can see it working.
Seems they had a version for the PDAs at one time. I just use the full blown version with the tablets. The problems I run into are the same no matter what software you use. Wearing gloves and such with the capacitive touch screens and good old water. Other than that, I have no problems with it. Of course you will want to design the panel based on the tablet you are using.
For working with sensors you probably need calibrator.
It have built in graduation of different standard sensors(k-type,100P,1000P and so on) and allow to create own equations for current loops or voltage signals. But it costs alot and it cant replace DMM.