hp8904a function generator floating impedance?

[sarepairman2]

I have 2 HP8904A units.


float measurements taken with 34401a, 10mohm input impedance setting
Supposedly good unit:
channel 1 to earth : 31k (functional light)
channel 2 to earth ; 1k (functional light)

supposedly bad unit (i think it just has a broken indicator light for float)
channel 1 to earth: 45k (good light)
channel 2 to earth : 16k (non functional light)


I hooked up a DC supply to the float control relay and found that if I put enough DC into it I can get the impedance between chassis ground and the supposedly floating thing to read High Z on my 10Mohm input z ohm meter.

Do these units both have faulty relays/relay controllers... or is floating >1Kohm considered good ? I figured float ment broken circuit, so a DC ohm meter should read infinity...

[sarepairman2]

and when its not floating the impedance to earth ground/chassis is 50 ohms as it should be.


SO WHAT is considered a reasonable DC impedance for a floating instrument?

do these units have a common problem of the relay supply rail current being prone to fuck up?

[tggzzz]

It isn't clear, but are you confusing "floating" with "isolated"?

[sarepairman2]

It isn't clear, but are you confusing "floating" with "isolated"?

eh, the front chassis says "float" and it has a little light that turns on when its floating. '

[sarepairman2]

basically if the float is off the Low terminal center conductor reads like 0.5 ohms to chassis ground (shorted). when float is on it reads whatever I wrote (both my instruments are dual channel).

the impedance between high and low center pins in float mode is ~50 ohms and I verified that it works as a fully differential amplifier output.

im making a seperate thread for signal integrity of this instrument!