Ground Isolation required? yes or no?

[OxFF]

When using sensitive measurement devices like RF probing devices, do you think an isolation transformer is required?

[Jeremy R.]

I am not completely sure what your question is. What type of system setup do you have or are questioning. Are our RF analyzers or generators part of the equation here? Please detail your question and I'll do my best to answer. Thanks.

Best Regards,
Jeremy R.
NI - Applications Engineer.

[OxFF]

It's simple an RF Signal analyzer connected via PXI (PXI-5660). The system is used to test manufactured wireless related devices in the 900Mhz range. The measurement rack will have power supplies, etc. to provide power to the loadboard (where the devices will be placed for testing). We've been running production tests like these without ground isolation for the measurement devices (isolation transformer), and I'm wondering if a dirty ground could effect devices similar to PXI-5660. Keep in mind this is a factory environment.

[OxFF]

Attention NI:

I think your company lacks application notes,whitepapers, documentation on the quality of mains power on your hardware. Maximum, TI, etc. have many documents that talk about common mode noise, galvanic isolation, ground ripple, ground loops, etc. I think it's even more imperative for NI to have similar documents (because of the nature of NI products).

[Jeremy R.]

Each PXI device in a chassis will be connected to chassis ground which is determined by the power source. Each PXI chassis does come with a safety ground in case a power supply does not have an appropriate ground. The manual for your particular PXI chassis can be found at:

http://digital.ni.com/manuals.nsf/MainPage?OpenForm&node=132020_US

I cannot say in particular what effects your transformer may have, but you will be able to use the safety ground if that is needed.

Best Regards,
Jeremy R.
NI - Applications Engineer

[OxFF]

Is it safe to say that most of your data acquisition systems have differential inputs with robust isolation from ground? I've had bad experiences (well I'm a new to test engineering, but I've seen gurus fall because of this) of destroyed systems or noisy systems because front ends couldn't float to common mode voltages. Has NI made these issues a standard when designing their hardware DAQ products?

[m3nth]

This is an old post but I had similiar questions regarding the PXI-5122 Scope card in a PXI-1045 Chassis.

As stated previously: NI documentation regarding the impedance of the scope-signal-returns to mains ground is lacking (basically, there isn't any. Not in the NI PXI-5122 specs I have anyway). But for reference, testing it with a DMM (powered on or powered off) shows a direct connection (< 3 ohms which may have been the DMM) both for return to PXI chassis and return to AC Mains.

That confirms both statements made previously in this post:
- The PXI Chassis is directly grounded to AC Mains -and-
- Be careful of how you take measurements the same way you would with an older scope that isn't floated off the AC Mains. Otherwise very bad things can happen 😉