EMC and Interfacing

Question 1

What materials should space connectors be made from?

Answer 1

Gold metals and PTFE. Connectors should have a metal shell to protect from EMI

Question 2

Why are circular connectors preferred to D-type connectors?

Answer 2

More robust connections, though if a higher packing density is required, D-type connectors are better

Question 3

What are the mechanical requirements of harnesses?

Answer 3

Need to be strong enough to deal with the stresses from launch, hence at least a 26 AWG is used, AWG should be kept minimal to conserve mass

Question 4

What strategies can be used to minimise EMI?

Answer 4

• Partitioning of harnesses for power, pyrotechnic, digital and analogue signals
• Using slow rise and fall times for digital signals, i.e. the minimum possible data transmission rates
• Using differential signalling to keep the voltages and currents at a minimum

Question 5

Describe how differential signalling can protect against EMI

Answer 5

two lines are connect to a differential amplifier, if you input the desired signal and its inverse, the differential amplifier will filter out any common mode interference and output just the desired signal

Question 6

How are power subsystems connected to the main power system to reduce EMI

Answer 6

1. All subsystems are grounded back at the main power subsystem, ie. via a common ground to reduce ground loops
2. twisted pairs are used to signal to and from the power main and subsystems. This reduces radiation from these lines
3. Isolation transformers/buffers are used at the interface of the subsystems to isolate external electrical behaviour from the subsystems

Question 7

Why is it important to measure the power consumption of the electrical sub systems?

Answer 7

Because power consumption changes might indicate system degradation resulting from damage from ionising radiation

Question 8

Describe the circuit used for digital input protection

Answer 8

two resistors, one immediately to ground to ground input when there’s no output, one for current-limiting
two diodes in parallel going to ground, one for preventing voltage going about Vss, another for preventing the voltage going below ground

Question 9

Describe the circuit used for digital output protection

Answer 9

same as input but with the two diodes making a divider between the two power rails