What's the difference between Rated Carry Current and Max Switching
Current? Which of these two should I consider as the current limit?
The rated carry current is always the higher figure - basically if you switch a relay on/off at its maximum carry current then you are doing the contacts harm - you should only switch at the max switching current. If that current then grows to the rated carry current that is fine but, before switching the relay off the current has to fall-back to the max switching current.
It won't instantly "fail" if you don't follow the rules but its life will be impaired and it will eventually fail sooner because of this.
I'm not a radar expert by any means, but I think I understand the general concepts well enough to try to answer your questions.
What specific requirements on the peak and average powers and the widths of radar pulses was chirped-radar designed to overcome? Were these purely 'internal' concerns regarding the electronics, or were there external goals and restrictions that were hard to meet otherwise?
The basic problem in radar is to get both adequate power for total range and good timing resolution for range resolution. It is hard to build high-power amplifiers for microwave frequencies. You want to have a lot of energy in each transmitted pulse, but you also want to keep the pulse short. The solution, as you have found in optics, is to stretch the pulse by chirping it, which allows the power amplifier to operate at a lower power for a longer time in order to get the same pulse energy.
Now, in radar, it doesn't matter if you don't compress the pulse again before feeding it to the antenna — the chirped pulse works just as well as the compressed pulse in terms of detecting objects.
In fact, you gain additional advantages when the reflections come back, because now you can amplify the chirped signal in the receiver (getting some of the same advantages as in the transmitter amplifier regarding peak-to-average power), and you can use a "matched filter" to compress the pulse just prior to detection, which has the additional advantage of rejecting a lot of potential interference sources as well. The narrow pulses coming out of the receiver filter give you the time resolution you need.
Is the name 'chirped pulse amplification' ever used in a radar context?
Generally not, because amplification isn't the only reason that chirping is used.
Is the optics-style CPA - stretch, amplify, compress, and then use the pulse - used at all in radar applications, or in broader electronics fields?
Not to my knowledge, but it would certainly be feasible.
Best Answer
The circled op-amp controls the loop current by controlling the base of the transistor Q1 or 'component 2'.
For example, if Vin = 0, the 100uA current source causes a 97.5mV voltage across the 975\$\Omega\$ resistor, which causes a 4mA output current ( 1 + 975/25 = 40). Similarly, if Vin > 0, then Io = 4mA + Vin(40/Rg).
The circled transistor does the same thing as Q1- controls the output current. If Q1 is present then it carries little current and Q1 takes over. If Q1 is absent the circuit will still function.
However, in loop-powered instrumentation the loop voltage can be quite high, so the power dissipation at full scale (30mA is possible) can also be quite high, so it's frequently desirable to offload that power dissipation into an external component that can handle the dissipation rather than have it on the same die as sensitive circuitry and may not be capable of the dissipation).