• Resolved

PGA900EVM: Higher current in 4-20 mA loop

Part Number: PGA900EVM

I am using pga900 EVM. I configured PGA 900 for 4-20 mA loop, but loop current is around 4.3mA even when DAC register value is 0!!!!!!

Linearty is holding good between DAC register value and loop current at higher values.

  • Hi Philip,

    In order to make the 4-20mA loop work on the EVM make sure that the following jumpers are set:

    J9, J4, J5, J10 - Closed
    J6, J8, J7, J16 - Open
    J19 - Set between pins 2-3
    J14 - Set between pins 1-2

    Jumpers J27, J28, J30, J26, J24, J25 - can be closed or open. These establish the digital communication (SPI, I2C) with the device. If these jumpers are open, the only communication possible is OWI.

    With this jumper configuration, the 4-20 mA current can be measured at test points TP3 and TP2 as voltage !!! (current across 10 Ohm Resistor on the EVM).

    In the PGA900 GUI the following Setting need to be set for the 4-20mA loop to be enabled.

    - On the "DAC & PWM Settings" Page.
    1. DAC_ENABLE = Enabled
    2. TEST_MUX_DAC_EN = Enabled
    3. Voltage Amplification = No Gain
    4. 4_20MA_EN = Checked (Enabled)

    Now if you write a value between 0x0000 and 0x3FFF in DAC_REG0, you should be able to change the current.

    If you follow all of the steps above and have 0x0000 code on the DAC, the current pulled by the device should not be more than approx. 3mA.

    Regards,
    Viktor.
  • In reply to Viktor Tasevski:

    Thanks Victor. My problem got resolved. The IC which simulated wheatstone bridge was drawing more current. I just simply removed that IC. Now syatem is working fine.