DAQ1300 Reading State Problem

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philip.wall
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DAQ1300 Reading State Problem

Postby philip.wall » Sat Feb 02, 2019 3:53 pm

Hello, I'm using the latest Python libraries with a Python2 build on Arch Linux. So far everything seems to be going good except when I'm trying to read a DAQ1300 channel.
I was trying to use it to determine if a wall thermostat was indicating it needed heat. Unfortunately I just couldn't get it to work. I believe it has something to do with the way the circuit is normally closed when not calling for heat.
So I switched it to reading the output on the Zone valve which is normally open and only passes voltage back when the end switch is closed. This seems to work except when reading the state of the channel it seems to rapidly switch between 0 and 1. I confirmed this by using one of the example programs provided.
If the switch is open it reads 0 with no state changes. If the switch closes the state rapidly starts changing from 0 to 1. A volt meter doesn't show any fluctuation of the voltage.
I further investigated by hooking a simple on off switch in the thermostat circuit and reading the state. Same behaviour, when open the state is 0. When closed it rapidly flips between 0 and 1.

Is this normal behaviour for the DAQ1300? How can I work around this? I just need to know when the circuit changes state from open to close.

All voltages are 24 VAC.There is no amperage to speak of.

philip.wall
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Re: DAQ1300 Reading State Problem

Postby philip.wall » Mon Feb 04, 2019 5:29 pm

Just thinking out loud here but could the issue be that I am using AC instead of DC current? And the constant flipping is due to the way AC cycles?

Is there a way I could get around this? I'm thinking possibly a relay. Needs to be something inexpensive.

jdecoux
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Re: DAQ1300 Reading State Problem

Postby jdecoux » Tue Feb 05, 2019 5:50 pm

The DAQ1300 is designed to work with DC signals, so an AC voltage source would cause the constant on/off behaviour you've been seeing.

There are a number of ways you could go about fixing this, either you could use a relay to switch a secondary voltage source, as you say, or you could get a 24V AC-DC converter with an output voltage between 2.5-30VDC.

berkinet
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Re: DAQ1300 Reading State Problem

Postby berkinet » Sun Mar 03, 2019 12:21 pm

Or... a simple diode bridge would give you 0 and 24vdc.


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