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Current source, 4-20mA Signal Generator - Test / Review / Opis

CMS 7098 46
This content has been translated » The original version can be found here
  • The inspiration for today's article was a colleague @kkknc who in the thread dedicated to gadgets that may appear in the Electrode shop , he proposed two interesting devices, and I quote: "Cheap and interesting. 1Hz-150KHz 3.3V-30V PWM Board Pulse Signal Generator Module PWM Frequency Cycle Operation adjustable Module LCD Display https://s.click.aliexpress.com/e/uPlEreh And the second suggestion. 4-20mA Signal Generator Load Current Transducer Tester PLC Instrument LCD Two Wire Output https://s.click.aliexpress.com/e/c2UH8aa9 "

    @Gulson I liked the idea, and I quote: "Thanks, I make a note to be checked by @CMS. That's what you need here, 50 points for you"
    and ordered one piece for testing.

    Let's move on to the presentation of the described gadget. At the beginning, a standard photo from the auction:
    Current source, 4-20mA Signal Generator - Test / Review / Opis

    As you can see, it costs a lot, about twenty three zlotys, but you should add seven zlotys for shipping.
    If they all have repeatable parameters and hold them like my copy, I can already say that if this gadget goes to the store, it will come off like hot cakes.

    I admit that after unpacking the new toy, I didn't really know how to play with it. In the description of the auction there is information that the set includes a user manual (which, unfortunately, I did not receive), and the picture shows that a resistor is needed.
    The device has only two "pins" on the rear panel and that would be enough for the connection.
    After a quick consultation with a colleague @Bestler , I found out how to bite it and after a while I was enjoying the new, very useful toy.

    I hope that with this device, I will take you another reason for whining when testing multimeters.

    The device works in a very simple way, you just need to connect the power supply from 15V to 30V and that's it (although the correct indications in my unit started only at 17V).
    For safety, I connected through a 470? resistor. Now it is enough to connect the device that we want to test in series with the power supply, for example a multimeter in the mile-Amp range.

    The device can also be successfully used in several other ways.
    - as a constant source of current signal with the possibility of adjustment and precise setting (with an accurate reading of what we have set). For example, as an offset for another signal,

    - for temporary simulation of sensors with current output, e.g. replacing the sensor at the time of its failure,

    - bearing in mind the accuracy of the displayed current to two decimal places and compliance with the actual state - as can be seen in the attached photos - we can use the tested set-point as a current source to calibrate analog inputs in all devices that have a current input.

    Unfortunately, despite two decimal places, the settings are not every 0.01, but every 0.05

    I must admit that I was very positively surprised by the results of the measurements. The test was performed with a Sanwa multimeter, which you have already seen while reviewing the reference voltage. So you know that there is a fairly accurate device, with a slightly higher than average shelf.

    Okay, I won't keep you in suspense anymore, you finally have the photographic material you want, because one image will convey more than a thousand words :)

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    This is how this gadget looks like. The panel casing begs to be mounted as an accessory, for example in a laboratory power supply.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    We won't find many elements inside.

    Well, we finally got to the tests, you have to admit that for a gadget for thirty zlotys, there is nothing to complain about.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis

    I also decided to check what the lowest and highest current I can set.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    Well, applause for the producer again.

    I can only fault one thing. The display has a backlight. Seriously, it's turned on in all photos (because there is no other option), and yet it is not visible. And it's not the fault of the camera, lighting, or my other mistakes. It is barely "going". Here's a photo where I blocked most of the light from the outside with my hand:

    Current source, 4-20mA Signal Generator - Test / Review / Opis
    However, it does not bother you at all, because the display in daylight is very readable, and when there is no light, it can be read anyway, even with such a weak backlight.
    However, it should be remembered that the whole thing with the minimum setting is to consume no more than 4mA, and as you can see, even 3mA is possible. With such a weak power supply, the manufacturer should be congratulated on the fact that, despite everything, somehow managed to illuminate this display.

    Summarizing:
    I am very happy with this gadget, the current given is very accurate and the price of the device is ridiculous. I think that this toy will permanently appear in my articles about all kinds of multimeters. Regular readers of my scribble know that I am trying to objectively evaluate the tested gadgets and, unfortunately, I am often forced to write that it is rubbish. This time, however, there is a case when I simply can't help myself and I just have to recommend you to buy this device, because it does the job so nice.
    You don't even know how much my morale has just increased ... Any day you will finally get the long-promised reviews of Q1 and Clamp ...

    Just as I thought the article was ready, a lively backstage discussion kicked off and thanks to that I did two more tests suggested by @Bestler By the way, it turned out that the problem with proper operation with power supply below 17V resulted from the use of a 470? resistor.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    Powering 15V through a resistor, as you can see 10mA is fine, but at 20mA we already have a big error.

    The correct result was obtained only at 20V:
    Current source, 4-20mA Signal Generator - Test / Review / Opis

    However, after getting rid of the resistor, it turns out that the system works properly at much lower voltages than declared by the manufacturer.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    As you can see, 10mA can be obtained with 8V power supply, and 20mA with 10.5V

    The first experiment was to set the value to 10mA and adjust the power supply to see if the result was stable over the entire range:
    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    Current source, 4-20mA Signal Generator - Test / Review / Opis
    As you can see, the circuit works fine.

    The second experiment consisted in setting the power supply to 24V and plugging in a 470? potentiometer. Then, setting the value of 10mA and checking whether turning the potentiometer has any effect on the set current.
    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis
    In the first photo, the potentiometer is turned to the extreme left position, in the second - in the middle position, and in the last, in the extreme right position. I did not notice any significant changes while shooting the peer.

    One more important piece of information, the Chinese, included the following information in the auction description: "REVERSE CONNECTION PROTECTION: Our digital signal generator can be inverted connected (two-wire system, no matter positive or reverse connection, the meter can work normally and will not be burnt.)"
    I didn't check it, but as far as my eyes are concerned, the D2 is a rectifier bridge (I don't have the device with me to check now).

    EDIT 01/21/2019, 16:50:

    As you asked about the possibility of including a resistor in the circuit to get a pseudo voltage standard, I am posting some additional photos with a 100? resistor, unfortunately I did not have such a 1%.

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis

    Current source, 4-20mA Signal Generator - Test / Review / Opis Current source, 4-20mA Signal Generator - Test / Review / Opis

    Best regards.
    CMS
    Can you write similar article? Send message to me and you will get SD card 64GB.
    About Author
    CMS
    Administrator of HydePark
    Offline 
    CMS wrote 6853 posts with rating 1756, helped 154 times. Live in city Warszawa. Been with us since 2004 year.
  • #2
    Szyszkownik Kilkujadek
    Level 36  
    CMS wrote:
    The device has only two "pins" on the rear panel and that would be enough for the connection.

    1. So it is simply plugged into the tested circuit in series and it does not need to be additionally powered?
    2. Is the polarity, plus / minus to which input device connection important?
    3. What is the minimum power supply current required? Although perhaps it would be more precise to know: what minimum power must flow through this setter to work properly?

    Added after 4 [minutes]:

    CMS wrote:
    The second experiment consisted in setting the power supply to 24V and plugging in a 470? potentiometer. Then, setting the value of 10mA and checking whether turning the potentiometer has any effect on the set current.

    4. I understand that this test was only to check if after pressing the knob, the setter actually remembers the set value and does not respond to turning the knob?
  • #3
    vodiczka
    Level 43  
    CMS wrote:
    If they all have repeatable parameters and hold them like my copy, I can already say that if this gadget goes to the store, it will come off like hot cakes.

    Are you sure "like hot cakes"? Despite good parameters and nice workmanship, its use is quite limited.
    If only it could give the reference voltage in the range 1-10V.
  • #4
    LChucki
    Level 31  
    vodiczka wrote:
    zy to be sure "like fresh rolls"?

    Probably not because a small group of interested parties - industrial automation. I would probably be tempted, because sometimes I do something on the current loop. Most often, an appropriate power supply and potentiometer + resistor are enough, but not always.

    Added after 44 [seconds]:

    vodiczka wrote:
    If only it could give the reference voltage in the range 1-10V.

    For this there are other setpoints. Sometimes a potentiometer is enough.
  • #5
    vodiczka
    Level 43  
    LChucki wrote:
    For this there are other setpoints.
    I know but we'd have "two in one" :|
    It could be two independent circuits on one PCB with one common display showing V and mA simultaneously.

    CMS wrote:
    Now it is enough to connect the device that we want to test in series with the power supply,
    What is the acceptable upper limit of the load resistance?
    Is it possible to load the room unit with a 100? 0.1% resistor and thus obtain the reference voltage in the range of 0.4 - 2.0 V
  • #6
    Szyszkownik Kilkujadek
    Level 36  
    vodiczka wrote:
    Is it possible to load the room unit with a 100? 0.1% resistor and thus obtain the reference voltage in the range of 0.4 - 2.0 V

    I join the question.
  • #7
    vodiczka
    Level 43  
    Szyszkownik Kilkujadek wrote:
    I join the question.
    I think that 100? is possible, since the minimum supply voltage is 15V and the maximum voltage drop on this resistance is 100? x 20mA = 2V but what if it is higher. What could be the biggest?
  • #8
    bestler
    Admin of DIY, Automation
    vodiczka wrote:
    Is it possible to load the room unit with a 100? 0.1% resistor and thus obtain the reference voltage in the range of 0.4 - 2.0 V

    You can, but you have to remember that the zero load capacity of such a "voltage source", any physical load of even a few kiloohms will lead to an error.

    vodiczka wrote:
    If only it could give the reference voltage in the range 1-10V.


    Insert a 500? resistor and you will have a voltage of 2-10V with the note as above.
  • #9
    kkknc
    Level 43  
    When called to the board, I answer that I liked this gadget, and I mean testing the circuits in all kinds of 4-20mA sensors. That's why I proposed it. More and more different types of sensors are entering into common use and the demand for such a miracle will be increasing. Of course, if someone wants to use it ......
    CMS usually did his best to the task entrusted to him and it is rather miracles that he will not stay on the shelves too long. Of course, as others have noted, it will not be a hit.
  • #10
    vodiczka
    Level 43  
    bestler wrote:
    Any physical load of even a few kiloohms will lead to an error.
    With a voltage drop across a resistance of 100?, additional resistance> 10k? will introduce an "acceptable error"
  • #11
    burur
    Level 19  
    In such a room unit it is sometimes useful to scale 0-100%, 4mA - 0%, 20mA -100%. I use a fast setter made on the LM317, additionally I connect a milliammeter, and here there are two in one, a setter and a milliammeter. Such a setter will work for quick tests.
  • #12
    CMS
    Administrator of HydePark
    Szyszkownik Kilkujadek wrote:
    1. So it is simply plugged into the tested circuit in series and it does not need to be additionally powered?


    Yes.

    Szyszkownik Kilkujadek wrote:
    2. Is the polarity, plus / minus to which input device connection important?


    I added information in the first post:

    CMS wrote:
    One more important piece of information, Chinese, in the description of the auction included this information: "SECURITY OF REVERSE CONNECTION: Our digital signal generator can be reversed connected (two-wire system, no matter positive or reverse connection, the meter can work normally and will not be burnt.) "
    I didn't check it, but as far as my eyes are concerned, the D2 is a rectifier bridge (I don't have the device with me to check now).


    Szyszkownik Kilkujadek wrote:
    3. What is the minimum power supply current required? Although perhaps it would be more precise to know: what minimum power must flow through this setter to work properly?


    I have no idea but I think no more than 30mA

    Szyszkownik Kilkujadek wrote:
    4. I understand that this test was only to check if after pressing the knob, the setter actually remembers the set value and does not respond to turning the knob?


    No. The potentiometer was connected in series and the purpose of the test was to check if the set current was stable during the change of resistance.
    Pressing the knob saves the setting and remembers the value after turning off the power.

    Szyszkownik Kilkujadek wrote:
    vodiczka wrote:
    Is it possible to load the room unit with a 100? 0.1% resistor and thus obtain the reference voltage in the range of 0.4 - 2.0 V

    I join the question.


    You can, provided you take into account what I wrote in the first post about the voltage drop on the resistor, which made 20mA stable only at 20V power supply.
    I am adding a few photos to the first post. Unfortunately, I didn't have a 1% resistor.
  • #13
    vodiczka
    Level 43  
    CMS wrote:
    I am adding a few photos to the first post. Unfortunately, I didn't have a 1% resistor.
    Perfect illustration of the answer to my question. Thank you.
    I think with a tolerance of 0.1% this would be a good amateur voltage pattern, not a pseudo voltage pattern. :|

    Only now did I understand that this system acts as an active load, forcing a current of a given intensity.
    At first I was confused by the first part of its name: "4-20mA Signal Generator ..." and I thought it was a kind of current source.
  • #15
    CMS
    Administrator of HydePark
    Sorry, I have already corrected.
  • #17
    User removed account
    Level 1  
  • #19
    mkpl
    Level 37  
    Nice equipment, although serial power has its drawbacks. After disconnecting from the target tested element (e.g. diode), the power is turned off and everything resets.

    What does "reaching" the set current look like? Are there any overshoots?
  • #20
    CMS
    Administrator of HydePark
    mkpl wrote:
    power goes out and everything resets


    If you remember the setting by pressing the pulse generator knob, then after a power failure, the value will be the same as before.
  • #21
    PiotrPitucha
    Level 33  
    Hello
    I had a little fun with calibrating automation devices and the principle was that we calibrate devices of a class better than the tested device, not to mention such a small thing as papers for the measuring device. It turns out that in order to research it is appropriate to have a 0.01% specter, and neither Dacpol nor the Chinese do not boast of such parameters, because it is cheaper for the Chinese people :) .
    The hardest job was to calibrate the temperature sensors, the cool Fluke for this purpose had a large aluminum block and it weighed way too much to carry around the scaffolding and cost more than my car, it was a fear to carry.
  • #22
    User removed account
    Level 1  
  • #23
    User removed account
    User removed account  
  • #24
    LChucki
    Level 31  
    dabek3456 wrote:
    you enter "excel online" in google and you don't even have to pay anything, I recommend that you familiarize yourself with this tool.

    How much do they pay for advertising?
  • #25
    User removed account
    User removed account  
  • #26
    LChucki
    Level 31  
    dabek3456 wrote:
    LChucki wrote:
    dabek3456 wrote:
    you enter "excel online" in google and you don't even have to pay anything, I recommend that you familiarize yourself with this tool.

    How much do they pay for advertising?

    $ 1,000 per post

    I do not want to believe me, give a link to this offer.
  • #27
    PiotrPitucha
    Level 33  
    Hello
    odalladoalla , neither PZL nor PRAT :) only the Netherlands and countless power plants (by the way, what they do with electricity as every few kilometers a power plant), both gas and waste incinerators.
    I don't know if my Fluke was heavier, it had quite a prominent aluminum block in the back and the auto-calibration lasted several minutes and the measurement was around a minute with drawing the heating characteristics and it was probably 0.002% but moments ago it was ...
  • #28
    kkknc
    Level 43  
    There are photos and everyone can see for themselves. According to the rule, one picture is worth 1000 words.
    @CMS took his time and I don't see any need for him to add it to another malcontent. You wanna do it do. Perhaps someone will benefit.
  • #29
    User removed account
    User removed account  
  • #30
    User removed account
    Level 1