RTCA Do-160 Section 16 Power Input - DC Ripple Testing 1

[jmootrey]

Hello Everyone,

I am looking for someone familiar with RTCA Do-160, specifically the DC Ripple test of section 16. The test seems identical to the Audio Frequency testing. In fact the DC ripple voltage points to that audio frequency as having all the test parameters. What is the difference in these two tests? Should only one or the other be performed?

 

[debodine]

The DC ripple test in section 16 is to determine the AC ripple riding the DC voltages inherent to the system design. The ripple must not exceed the limits based on frequency and these limits are found in the referenced area of section 18. The assumption by the design team is that if the ripple remains at or below limits the unit under test can perform its intended functions.

The audio frequency test in section 18 is energy that is deliberately introduced from the outside world (the test setup) into the power input lines. The ripple being forcibly introduced is set to those limits and the unit under test must still perform its intended functions.

The difference is the first test verifies internal ripple generated by the unit under test is within design limits and the second test verifies the ability of the unit under test to reject or ignore the ripple introduced from the (simulated) environment where it will be expected to function.

 

[jmootrey]

Thank you for the reply! Would the test than only be considered for power generating equipment? If not, how does one isolate the ripple created by the power supply vs additional ripple created by the EUT? How would one isolate the various frequencies during a ripple test, or is specialized equipment required?

 

[debodine]

It has been years since I did some testing in the DO-160 cage, but as I recall here are the answers I would give you:

The DC ripple test is to make sure that ANY equipment installed does not internally generate and impose ripple on the power distribution system greater than the test limits specify. The type of equipment is immaterial. In other words it is not limitied to power generatiing equipment only. Any equipment installed on the power distribution system is not allowed to introduce ripple onto the power distribution system in excess of the limits, and the purpose is to protect all other units installed on the power distribution system as well as protect the power distribution system itself.

There is no need to isolate the ripple coming from the internals of the unit under test when performing the AF test. Whatever ripple exists from inside the unit under test is already there and considered to be the normal working environment of the unit under test. You set the externally introduced ripple energy to the specified levels and apply it. What the power input lines of the unit under test will be experiencing is the externally introduced AF plus the internally generated ripple, which is the "real world" scenario that you want to test.

For example lets say the unit under test has an internally generated ripple of x. Then when you perform the AF test, assume that you are instructed to externally introduce AF at a magnitude of y. During the AF test the power line with the externally introduced and internally generated ripple will experience total ripple/AF energy of x + y. For the purpose of this illustration I am ignoring phase and frequency but in real life the waveforms will not add in a linear manner unless your test setup sychronizes both phase and frequency.