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HP Forum Archive 13

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HP 3421A actuators
Message #1 Posted by Tracy Vermeyen on 22 Aug 2003, 12:43 a.m.

I have a HP 3421A that I have repaired and I have a question about the 10-CH multiplexer assembly (Option 20)boards. What applications are there for the actuator's channels (channels 0 and 1)?


Re: HP 3421A actuators
Message #2 Posted by Andy on 22 Aug 2003, 5:51 p.m.,
in response to message #1 by Tracy Vermeyen

I have used the actuators to activate relays so I can turn higher voltage devices on and off.

For example, I once hooked a humidifier up to a relay controlled by channel 0 on the 3421a. Then I had two thermocouples to measure both wet bulb and dry bulb temperatures. I used my hp75 to calculate relative humidity from the two temperatures (and a known air pressure) and then had it turn the humidifier on or off to control humidity.

Also, I have a freind who uses his 3421 and his 41cx to control his home sprinkler system (I think he has the digital card option though which gives you more on/off channels). He uses a repeating alarm on his 41cx to call a program which opens and closes valves.

The possiblities are endless!



Re: HP 3421A actuators
Message #3 Posted by Tony Duell (UK) on 22 Aug 2003, 6:23 p.m.,
in response to message #1 by Tracy Vermeyen

OK, the 10 channel input board has 10 (electromechanical) relays on it. 8 of them (channels 2-9 IIRC) are connected to the input of the ADC section, and can only be used as 'multiplexers' -- to switch different signals to the ADC so that you can, for example, measure input and output voltages of a circuit. The other 2 can be set by links on the input board to either be multiplexer channels, or 'actuators'. The latter means the contacts are not connected to anything inside the 3421 (apart from protection networks IIRC), so you can use them to switch external circuits. Be warned the contacts can't handle much current or voltage -- use them to switch a larger relay if necessary.

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