[Amps] Monitoring temperature

[Manfred Mornhinweg]

Bill,

> I would appreciate any suggestions for monitoring temperature on a solid
> state power amp. 

In addition to the chip you used, there are many other options. There 
are some digital temperature sensor chips, like the DS18S20. I have used 
that one in several professional projects. It's very useful when you 
need to put the temperature data into a microcontroller, specially when 
you need to measure the temperature at different places, because you can 
connect several of these sensors using a single wire, and program 
addresses into the sensors to access them selectively.

If you are after simpler things, look at thermistors, which don't tend 
to rectify RF. They exist in PTC and NTC versions. They are very 
non-linear, and that limits theri usefulness in some cases, while in 
other cases it can be an asset.

Also look at Pt100 and Pt1000 sensors. They are almost linear, highly 
accurate, RF-insensitive, and exist in many physical shapes. But their 
output signals are small, so a lot of amplification is needed.

Don't overlook plain simple diodes and transistors as temperature 
sensors. A transistor connected as superdiode (joining base and 
collector) is best. The temperature coefficient is quite linear. I have 
used 2N2222 transistors as precision temperature sensors!

And about the high level RF in an amp, it's a matter of proper 
bypassing, perhaps a ferrite choke here and there, and in the worst case 
you might need to install a shield over an RF-sensitive IC sensor. The 
readout electronics should anyway be in a shielded compartment, using 
pass-through capacitors for the wires. Since temperature varies slowly, 
filtering the leads of any sort of analog temperature sensor is really 
simple. You don't need to pass any fast signals, so you can use any sort 
of brute force filtering.

I don't think you want to look into quartz temperature sensors! They are 
ultra accurate and stable, but not very common, and require a more 
complex readout circuit.

In most cases either ICs like the one you used, or like the DS18S20, or 
small cheap transistors are the most practical solutions.

Manfred

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