PPK2 not showing correct measurement

[vcarlon]

I seem to be getting a measured value of 1/10th of the actual current value.

On my original setup, I was expecting around 1mA of current, but ppk2 running in ampere meter mode is only measuring around 100uA. I connected another ammeter in series to test my hypothesis the other ammeter is measuring my expected value of around 1mA.

I created a very basic setup with just a 3.3V supply, 3.3K ohm resistor and the PPK2 connected in series to demonstrate the problem. This should also produce around 1mA of current, but the PPK2 is measuring only around 92.8uA (around 100uA). 

This is the screenshot of the PC application:

The circuit diagram:

And a picture of the setup:

I guessing I have a setting or a connection that is wrong, but I have checked everything as far as I can, and I can't seem to find it.

Thanks in advance for any help!

[hmolesworth]

The connection is incorrect: Place the load (3k3 resistor) from Vout to Gnd. Battery goes to Vin and Gnd. Both Gnd pins are connected together as you have them.

The PPK2 in ampere mode measures current flowing out of Vout towards Gnd, through the 3k3 resistor. That current is sourced from the battery on Vin.

[vcarlon]

It works as expected now. Thank you very much!

I thought it was measuring the current flowing through it just like the others ammeters, but apparently, it is only measuring the current flowing through the devices after the Vout pin.

Our actual board would thus need a rework for this fix.

[hmolesworth]

You might find my notes useful; I did these a while back when I was testing measurement ranges on the PPK2 (PPK-II)

// Resistor Rc for current sense is 1k0 in parallel with one or more of 110R, 11R0, 1R0 and 0R051
//
//              <- +ve Supply to DUT From VOUT                               External Battery +ve To VIN
//             +------------------------------+                             +-----------------------+
//             |                              |                             |                       |
//             |              +---------+     |                             |     +---------+       |
//             |              |     GND |     | VOUT                   VIN  |     | GND -ve |       |
//   +=========O=========+    |    +====O=====O=============================O=====O====+    |       | Battery
//   |        Vdd (+)    |    |    |    |     #----+                        |     |    |    |       | + 3 volts
//   |                   |    |    |    |     |    |Rc        AMPERE \      |     |    |    |     +-O-+
//   |                   |    |    |    |     |   +++                 \     |     |    |    |     |   |
//   |                   |    |    |    |     |   | |   +-----------O  O----#     |    |    |     |   |
//   | Device Under Test |    |    |    |     |   | |   |                   |     |    |    |     |   |
//   |       DUT         |    |    |    | 120k|   | |   |                   |120k |    |    |     |   |
//   |                   |    |    |    |    +++  +++   |   \  SOURCE      +++    |    |    |     |   |
//   |                   |    |    |    |    | |   |    |    \             | |    |    |    |     +-O-+
//   |                   |    |    |    |    | |   +----#--O  O-- PPK LDO  | |    |    |    |       | Gnd (-)
//   |                   |    |    |    |    | |                           | |    |    |    +-------+
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     |                             |     |    |
//   |                   |    |    |    |     #-- VDUT                VIN --#     |    |
//   |                   |    |    |    |     |  Sense                Sense |     |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     | 30k                     30k |     |    |
//   |                   |    |    |    +--#--+                             +--#--+    |
//   |                   |    |    |       |                                   |       |
//   |                   |    |    |     =====      <<== Common Gnd ==>>     =====     |
//   |                   |    |    |      ===           (Common -ve)          ===      |
//   |        Gnd (-)    |    |    |       =                                   =       |
//   +=========O=========+    |    +===================================================+
//             |              |     PPK-II
//             +--------------+

[vcarlon]

Thanks again! This is indeed very helpful