Signal generator voltage on power up

[Mike Fikes]

I got a new signal generator and I noticed that when powering it on it drives the output to -10 V for about a second.

Is this normal? I presume this could damage components you might be testing if you have the generator connected at power up.

Is it standard practice to power up lab equipment (and power down) without any equipment connected to the circuit you are working on?

[Mike Fikes]

The attached shows a trace of the described behavior. The signal generator is a DG1022Z, with output channel one connected directly to the scope using a BNC cable, and with the scope channel set to 1X.

[spec]

Hi Mike Fikes

I got a new signal generator and I noticed that when powering it on it drives the output to -10 V for about a second.

Is this normal? I presume this could damage components you might be testing if you have the generator connected at power up.

I can't answer specifically for your Rigol DG1022Z but, in general, no that is not normal and is unacceptable. And yes, it definitely can damage your unit under test (UUT).

Is it standard practice to power up lab equipment (and power down) without any equipment connected to the circuit you are working on?

Not too sure what you mean here but I will cover all combinations.

Test equipment, apart from possibly specialist types, can be turned on and off with no UUT connected to them or with a UUT connected to them.

In strict theory test equipment should be turned on and then connected to the UUT, but nobody does this.

In a typical set up you may have a UUT connected to three PSUs, a scope, a signal generator and frequency counter say. The monitoring test equipment is not critical. But the PSUs are critical and you would need to check what the UUT requires. There are also situations where a UUT may be stressed if a signal source were connected but the PSUs were not.

The switch on negative output of your Rigol DG1022Z, reminds me of the time at work when we started getting a load of UUT failures, until we discovered that the lab PSUs we were using outputted a 70V spike at turn on.

[Mike Fikes]

Thanks for confirming and helping a newbie out!

Attached is another confirmation, a snapshot taken at the right moment, using a multimeter, just to be sure I didn't botch the measurement.

I'm assuming the -12 V could definitely be bad news for any TTL or other components you might have on a breadboard if you unfortunately powered up with it connected.

Will follow up with the vendor...

[mvs]

I'm assuming the -12 V could definitely be bad news for any TTL or other components you might have on a breadboard if you unfortunately powered up with it connected.

It depends on output impedance of your signal genenerator in this mode. It might have high-Z output with some leakage to Vee rail.
Make a check with say 1K resistor as load.