Questions regarding building my first instrument control system

[achb]

Hello, I have never built a control system from scratch before so I need some assistance in determining what kind of hardware I need to use. I have three instruments, which use combinations of BNC and RS232 serial for data output, and use RS232 serial for inputting commands to the instruments. I am building a system that monitors the outputs and sends inputs. Now, I am on a very limited budget. What kind of hardware do I need? I've looked through the National Instruments website but I'm still confused.

[Dennis_Knutson]

You just need a serial port for each instrument. What is confusing about that? USB-RS232 converters are cheap. I've had the best luck with converters that use the FTDI chipset. NI sells some as well but they are a bit pricey.

The BNC connectors on your instruments are not relevant to the control of the instruments. They would connect to your system and the design is up to you.

[achb]

I need to be able to monitor the outputs of the instruments since the commands to the instruments depends on it. Would that require a DAQ? All of the ones with BNC connectors are prohibitively expensive.

[Dennis_Knutson]

And you don't trust the instrument to accurately respond to commands?

If you truly need done sort of external feedback, then yes, you will need a device (or devices) that can measure the outputs. I have no idea what sort of device since you have not provided any details at all. Terminal blocks with bnc connectors are available. How can something be prohibitively expensive when it should have been included in the budget when the system was being designed?

[achb]

They are custom made instruments that BNC outputs that give a voltage that corresponds to some measurement. What other kind of details can I give you that would be helpful? As for the budget, _this_ is the system being designed so if it exceeds the budget then it probably just won't be built. Thank you for your quick responses so far. Are the terminal block bnc adapters you are referring to like these ones? https://www.google.ca/search?q=terminal+block+bnc+adapter&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjz8sb...

[Dennis_Knutson]

So you need to monitor some measurements or sources? A BNC connector on an instrument would normally be connected to to your system as a source or connected to a source of the system to measure it. The instrument source would be programmed with the remote commands (i.e. via RS232). A measurement that an instrument takes would be read by remote commands. How you connect to the system being tested is up to you and is part of the system design. If the instruments do not have the ability to output a measurement over the remote connection, then you need to know the type of signals that are being output and the type of connector is one of the less important decisions you need to make. You need to think in terms of voltage, current, frequency, etc. in order to pick a DAQ device. This is just basic. A 0-5 volt dc signal requires something different than 0-24 volts or 4-20ma. A 1kHz sine wave is different than a 100 kHz one. The number of signals you need to measure is also important.

Do you have anyone there that is familiar with electronics and basic measurement techniques? This forum is not appropriate for doing the low level design that needs to be done. That's a job for an engineer familiar with the system you want to control/test.