Jump to content

How To Test 0-20mA Bricklet


thicks

Recommended Posts

Hi,

 

I am trying to accurately test the Industrial 0-20mA Bricklet for a 2 wire application.  My application will be using 24VDC for excitation with a 0-20mA Pressure Transducer.  (Pin 1 +24V Power Supply, Pin 2 0V Return to Power Supply, Pin 3 to Transducer Excitation, Pin 4 Signal from Transducer). 

 

To test the accuracy of the Bricklet, I was thinking of renting a Keithley 6220 Current Generator BUT I am not sure how I would wire thise into the bricklet.  A Current loop Simulator might not be accurate enough.  I am looking for an input source that will allow we to select current at 16 bits or 0.00061mA.

 

If anyone has a good idea of how to accurately test the Bricklet then let me know. Please send wiring diagram of setup.

Current_Loop.jpg.2c43138319774374bad4cbb1af0a6e61.jpg

Link zu diesem Kommentar
Share on other sites

Generating a very precise current is a harder then measuring current precisely.

 

So one way may be to just connect a sensor or similar and to measure the current with a good multimeter or through something like a uCurrent for the actual value. This way you should be able to get a few Bricklet/real measurement pairs and to calibrate offset/gain if necessary.

 

The Bricklet itself relies on the accuracy of the used parts (datasheets can be found on the Bricklet page) and is not calibrated additionally.

Link zu diesem Kommentar
Share on other sites

I might try the uCurrent.  Thanks for the advice borg.

 

I was able to set up a voltage divide circuit with a 1.2K Resistor and a 5K Potentiometer.  I can adjust the potentiometer and see the current change between 4-20mA with "Brick Viewer". 

 

Is there an easy way to modify the 0-20mA bricklet firmware so that I could do the following:

See more digits in "Brick Viewer"

Change the resolution to 18bits on the MCP3423 ADC.

Output just the raw Analog to Digital Converter data.

 

I have the processes for modifying the Bricklet firmware working.  I am hoping that I could be directed to the place in the code where I could make these modification.  Also, is it possible that a Red Brick could help me with this?

 

Any help would be appreciated.

Current_Loop_02.jpg.23e14075ebb1a41abc9d189009a1a777.jpg

Link zu diesem Kommentar
Share on other sites

To change the resolution to 18 bits you just have to change the samples per second to 4 (which is default).

 

To get the Analog Value you have to change line 212 of 020ma.c from

ret_na = measurement*15625/91;

to

ret_na = measurement;

 

Alternatively you can just multiply the current that you get by the Bricklet with 91/15625 to go back to the analog value.

Link zu diesem Kommentar
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Gast
Reply to this topic...

×   Du hast formatierten Text eingefügt.   Formatierung jetzt entfernen

  Only 75 emoji are allowed.

×   Dein Link wurde automatisch eingebettet.   Einbetten rückgängig machen und als Link darstellen

×   Dein vorheriger Inhalt wurde wiederhergestellt.   Clear editor

×   Du kannst Bilder nicht direkt einfügen. Lade Bilder hoch oder lade sie von einer URL.

×
×
  • Neu erstellen...