Digi neo 8port pcie voltage level

we have Digi Neo 8port PCIe (P/N: 77000889 / S/N:R21216426 ) card and we have problem with the ModBus serial connection. We are trying to use card in Dell PowerEdge R720 with 1 CPU.

I assume there is something to do with the voltage level about Digi Neo port.

I measured something like 8.8Vdc from RS-232 D9 pins 4(TxD)-6(GND) when RS-232 D9 other end is connected to Digi Neo card through AccelePort.

I think this can cause some problem to later on when the RS-232 in changed to RS-485 when connecting to the PLC. Computer own serialport voltage between 4-6 pins is 5.4Vdc and with this port I can get connection to PLC.

This is quite unknown territory to me - so I’m asking can this PCIe card voltage been low down somehow or do you have different kind off card that operates lower voltage level?