Brad, the downhole cable is single-core within a metal tube. We have to transmit data over the same cable as there is only effectively 2 wires, the core, and the metal jacket...
Hi Keith,
I also wonder what will happen when it rains and the water completes the circuit, albeit a higher resistance one but a possible electrical circuit no less.
We might be able to make a custom insulator and similar to those high voltage insulators on higher voltage cables, design it so...
> The two statements make it unclear to me. Is the 24Vdc power for the signal connected to the VSD ground or not?
I found out that it is connected to the VSD ground. Isolating it makes no difference.
>Might be a pain in the you know what, but try replacing the bad sensor with a known good one...
Just for reference of how bad the VSD noise is, the 2 images here show the digital transmission from the downhole sensor before and after the VSD is started. The isolated handheld scope was connected across the power and ground connection. We transmit data over power as the cable is only single...
Keith, this is a wellhead for an oil well and we have 2 sensors. One is located 900 meters underground in the well measuring the pressure of the oil above the pump. The other sensor is located at the surface measuring the annulus pressure in the well. We subtract the annulus pressure from the...
Just a quick update on this issue, which is still not resolved. They replaced the 150m of rubber cable with a proper screened twisted pair. With the shield grounded at the VSD and the sensor in air, the signal is +-0.1 psi change so this looks good from the point of the data logger is able to...
Thanks Keith,
The issue is that the complete wellhead is mechanically connected to the motor housing and so is electrically bonded to the rest of the metalwork. The sensor is plugged into this wellhead so the body of the sensor is connected to the VSD ground via the wellhead. The 2 wires of the...
As a follow-up, I received a test sensor of the exact same model and it is stable when connected to our data logger in the workshop. No change in the out when the test VSD is running but mind you, that is only a 2KW version for workshop testing.
The client is now sourcing some screened twisted...
We have a custom built data logger with 4-20mA inputs that when tested with a current loop calibrator, the input is stable to 2 decimal places with the 3rd decimal fluctuating around +-0.003mA. The input has a 100 ohm resistor from the ADC input to ground. The ADC is a very stable 16 bit with...
