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Author Topic: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL  (Read 6639 times)

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Phyllomedusa

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Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« on: November 29, 2012, 05:56:32 PM »
Hey fellows,
as Kiriakos already had a review about the Agilent Process calibrator I think I'll give you a few words about mine....as a kind of small review.
Don't expect em to take it apart or blow any fuses, as that buddy is pretty expensive (when new). Nevertheless, I got it slightly used washed up on the shores of the bay....ebay....

As first introduction (deeper insights will be written later on), let me explain the features and why I have it:


The Metrahit Cal is the smaller brother of the Metrahit Multical/Metracal. Instead of a DMM/Calibrator mix the Metrahit Cal is just a source. So you'll generate voltages currents and so on with it and measure it with the device yo want to calibrate.
Kiriakos has shown the Processmeter which is a combination of sourcing/measuring device. I also had the Agilent in mind (and am pretty sure I bookmarked the Ebay.co.uk offer a while ago), but then came across the Metrahit CAL which seemed to suit my needs much better.
Entry calibrators just offer you a 0-24mA source to test 4-20mA loops and so on. The next level are V/mA calibrators which add the functionality of Voltage sourcing. This normally goes up to 10 or 15V for a Handheld device.
So that would be what the Agilent Processmeter could do as well.
My attention was attracted by the RTD and Thermocouple and Ohms simulation. So I can use the Calibrator to simulate a Thermocouple (J,K,L,n,R,S,t,u,b,E) or RTD (PT100, PT1000, Ni100, Ni1000) or just use the Ohms to test resistance (but only up to 2k Ohms). It can generate Frequencies as well. This can be done from 1 to 1k Hz in 0.1 increments. The Amplitude can be set as well (in the same Ranges as Voltage).
A pressure source would be neat as well, but I won't use that very much and so I can save a lot of money as these are much more expensive when added.
With the Metrahit CAL I can now check our logger systems if they are still in specs. As deassembling the station uses a lot of time and the calibration at factory is pretty expensive and takes a lot of time. The loggers itself are very good and rugged...so a self-check is the fastest and easiest way. You can then send them in if they are off, or just accept a small additional error.
I still have some CR1000 loggers around which we want to refit for student's use...so the Calibrator shall give me some nice help here ;). Also it is nice to test or working systems if there is any trouble.
For example: The Psychrometer is showing a wrong reading on one sensor....just plug it off, attach the Calibrator and simulate a PT100 on both channels and you see if it's a problem within the logger/internal wiring or the attachment cable/sensor itself.

....more (including colorful pictures) to come.....

Phyllomedusa

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #1 on: December 02, 2012, 06:03:16 PM »
So let's get started:

As I opened the package and placed the Metrahit Cal in my Hands for the first time it's been some of these "wow" experiences.
The Built quality is excellent and actually feels even a lot more rugged than my U1272A (and we know, thanks to Kiriakos, that this is a tough companion). The Metrahit Cal would fit more in the Category "Tank", but I wont give any references like that here ;).
The rubber-gurd can be easily removed and feels sticky and firmly in your hands. So if you just use it in your Lab, you could remove that one and the Metrahit Cal is much smaller and more like a Multimeter.
The rubber guard let it feel quite big and chunky and it will take some space in your toolbag.
Big plus-point: The calibrator is running on four AA batteries. You can get them or some decent eneloops everywhere and don't need to worry.
The runtime is between 8h (as mA source) and 45h (mV and TC), which should be useable in the field. GMC claims it to have 0,05% basic accuracy on most modes.   Just as RTD source this goes up to 0,1%, which is still fine.
Talking accuracy.... The Metrahit CAL comes DAkkS (formerly known as DKD) calibrated which has some tighter regulations than an ISO calibration. Nice to have, or as professional, you may even need a proper calibration due to legal regulations. As Hobbyist.....nice to have and it gives you some kind of trust.
The Display is pretty nice with big displays, but as a calibrator it isn't filled with too much information anyway.
If wanted, you could buy a (very expensive) USB cable and Software and control it from your PC and set up several Calibrators, as they can have a Network address. Well, don't spend the rediculous amout of money and set it up by hand.

Let's talk functionality:
The Voltage source has four ranges: 0-±300mV, 0-3V, 0-10V, 0-15V with an maximum current draw of 15mA. At 18mA the Calibrator will shut the sockets off to protect itself. You can remove the wires then and shut it on again and nothing happened.
The Frequency source goes from 1Hz to 1kHz in 1 Hz increments (feeling like a robot with all the 1's now) and has a fixes duty cycle of 50%. The amplitude can be set in the same range as the Voltage source (0-15V). So there is no pulse width modulation what is a bit sad and could be useful. For that purpose I still need my Function generator. The max. current draw is 15mA again.
The current source can work in three ranges: 4-20mA, 4-24mA and 0-24mA, where you can source up to 20V out of it. Well, it is a constant current source, so you'll have a limited load here (of course).
The Metrahit Cal can also work as current sink, what means it will lower your circuits current for about the specified current. Well, this is more or less a negative constant current source. You have the same ranges here like in the normal current source mode.
The resistance simulator can go from 5 to 2000Ohms in 0,1Ohm increments. You can apply a maximum source of 5mA through the Calibrator.
So as we already had the mV and resistance sourced, it is quite obvious that you could also source RTD's and Thermocouples. It can simulate a PT100 (-200 to +850°C), PT1000 (-200 to +300°C), Ni100 (-60 to +180°C) and Ni1000(-60 to +180°C). This can be pretty handy if you want to test a temperature control loop or so.
Thermocouples can be simulated in a variety of types. Look up the Manual for the ranges ;).

Two nice features are the Interval setup, where you can specify a Range, the number of steps and duration of a step and the Calibrator runs these up and down. So you'll just need to watch the reading of the tested meter, logger, A/D converter or whatever. As you know, or should know, which steps will be used by the Calibrator.
The second mode, ramp, is a bit different as it isn't using steps, but a continuos ramp where you specify the time it rises, it stays on the top level and the time to lower again. Personally I prefer the Step function as it is more controllable than the ramp.
I have two scope patterns for you to show these modes.

So all in all...it can be very handy, but probably you don't need one :-D. It may help you when you design a lot of circuits or control loops or when you have to maintain that stuff. I just used it today to have a look on the A/D input on one of my arduino's.... as expected it's not top notch, but can be used at least ;).
Today I got an email from my Chief, so it seems I will use it more often in the next weeks, as I will refurbish some equipment (Loggers and Sensors) and set them up in Taiwan next March. So I'll have fun with the Metrahit Cal within the next weeks ;). It seems my Agilent's will have a trip home next year :D.

I hope you don't mind the shit*y picture with small DOF and lots of moiré. It's been pretty dark and I needed to creep-in a lot onto my Display. ;)

Offline Kiriakos GR

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #2 on: December 03, 2012, 09:55:31 AM »
If you do not add more pictures about the Metrahit CAL exterior (like front and back) do not expect from us to pay you for this review ...  ;D ;D ;D ;D
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Phyllomedusa

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #3 on: December 03, 2012, 11:15:18 AM »
OK....you want it?.....you got it!

I have to correct myself. It is running on two AA batteries. Sorry for the mistake. I just opened it once to plug-in new batteries.

The rubber holster is big, but nice. It has a nice and stiff stand and an integrated clip to hang it somewhere. If you want/need, you also have an input jack for a power supply on the top of the calibrator.

Pictures:
- Calibrator in Rubber-Holster
- Bare calibrator (No stand on the CAL itself, just on the Holster)
- Battery and Fuse compartments (Yes, Kiriakos, no Eneloops inside yet ;))
- Rubber Holster stand and flip-out clip


Offline Kiriakos GR

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #4 on: December 03, 2012, 03:36:12 PM »
Now it is much better ..  :)

At the top of it, it looks to have also the DC input / External supply jack, which is great.
The Agilent one haves that just for charging, but due the enormous amount of rechargeable batteries in it, it can do more work prior needing a recharge.

Basically it is not possible to do an actual comparison of the two instruments, its one has its own strong points.
Congratulations about getting it.
But I am a bit jealous about your future travel in Taiwan.  ;)
Lets hope that it will involve more pleasure than work.
 

   
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Phyllomedusa

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #5 on: December 03, 2012, 03:59:42 PM »
Yes, it is a DC Jack....but (there is always a but). This DC Jack is only used to run the Calibrator, not for charging. When the cord is plugged in, the batteries get disconnected so that the calibrator is running from the mains.
So you'll have to charge the batteries externally. That's fine for me, but therefore I don't need the power adapter to work on my Bench.....it's a Handheld ;)

You are right that these two are separate devices. A big plus on the Agilent is the Multimeter function (someone can't ever have enough multimeter ;)....me ). Also that you can select several pulsewidth's on the Agilent, which could be handy to test servomotors or so.
My attention was attracted because the RTD and Thermocouple simulation. When setting up a new Climate Monitoring Station, this feature (well, more the RTD Simulation) can be quite handy to check the wiring or logger accuracy.


About Taiwan: well....that one got me out of nowhere. I didn't even hear any rumors that we will be working in Taiwan. So I'll need to read the project description and talk a lot to figure out what we will use there in the end.
The Fog sensors (which we don't have and which are pretty expensive) could be interesting. I don't know about the funding, but as they only need to give us Fog/No Fog and we have some decent visbility sensors.....DIY could be a solution.
I expect us to be in the middle of nowhere (as usual). But Taiwan seems to have an amazing countryside....that's mostly what matters ;)

Phyllomedusa

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Re: Multifunction Calibrator: Gossen Metrawatt Metrahit CAL
« Reply #6 on: December 21, 2012, 10:14:03 AM »
.....Well fellows, another of our trusty Campbell Sci CR1000 Dataloggers had been tested. I used my Metrahit CAL for that purpose and I really liked the Interval feature here.
I wanted to have a quick overview if any of the channels is malfunctioning or off, because when I disassembled the Station and opened the enclosure, I got a little shower! The enclosure wasn't opened for some years and there is an internal battery charger (solar charger) installed. The enclosure is sealed (IP67), so my guess is that the heating and cooling of the battery together with the sealed enclosure has built up some condensation which gathered in the enclosure over the years. The tropic climate may have helped a lot in this process.
Our partly open enclosures were all well.... So you can guess that I was a bit afraid when the station wasn't running anymore with all the water....

Good things first. The Logger is still working fine and not out of specs! So once again Campbell Sci impressed me with their rigidity. So I really can recommend that stuff if anyone is searching for a stand alone logger! *thumbs up*....they are tanks! (Logger info on http://www.ittsb.eu/forum/index.php?topic=196.0 )

So I took my Metrahit cal, set it to the according range ( I didn't use the Autorange feature of the logger....actually never needed it), and set up an Interval. I then just let the Calibrator do it's work. When I start on 0mV and end at 250mV with 6 steps, I know that each step is 50mV. Set the time to five seconds and let that fellow run. Now just lean back and wait for the reading on the logger (it was streaming the data to my laptop for that purpose). Five seconds was enough to write down notes and so on, but it could easily be set to a shorter or longer interval.
Nice!!!
Just out of curiosity, I took one of the PT100 bridges, screwed it in, programmed the logger for it and checked with my Metrahit Cal. -> Flawless as well.
Give out a Squarewave to check the pulsecount feature -> working as well as expected.

So once again..... The Metrahit CAL is damn expensive for a toy, but sometimes can be pretty handy. It'll be in good use in our Lab I guess. Let's see.... It will be in my toolbag for the fieldwork in Taiwan....That's for sure!


 

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