What terminal should I use as the return when using the Analog Out Ao terminal? I thought Sr looked most sensible and with my present experiment it seems to work fine - is this preferred?

Pg 148 drawing makes Ac look like a good choice, and maybe using Ac or even Sp I could create (differential) output voltages greater than 10 V this way if I wanted. Are any of these bad choices? Why?

Thanks!

Good morning Chris,

The only return for the Ao channel is the SR. the output is a maximum of +/- 10 VDC.

Cheers,
Roger

Hi,

It never occurred to me to check if the DT800 had an analogue output, but now that I know, I'm wondering if you could use it to simulate a thermocouple?

Specifically, I'm trying to convert a type-N thermocouple signal to type-R. Given that type-R 0.5 mm wire is $800/m, I'm very keen!

I can imagine this working by reading a type-N TC connected via one of the analogue inputs, and then using the temperature reading to generate the appropriate voltage on the Ao terminal.

Thoughts?

Good evening Chris,

No. It doesn't have enough resolution for that.

I use a Lithium battery with a 10 kOhm pot as a voltage divider to simulate the inputs.

Cheers,
Roger

Hi Roger,

I'm not sure I understand you exactly. Are you saying that you use the battery and pot in addition to the Ao terminal to simulate thermocouples, or just the battery and pot to simulate a thermocouple for testing analogue input terminal?

I see your point about the native resolution of the Ao terminal (10mV according to the manual). Type-R thermocouple demonstrate thermoelectric voltages between -0.226 and 21.101mV. Could additional hardware not bring the voltages down to this range?

Cheers,
Chris

Hi Chris,

I don't use the analog output at all. Simply a battery and voltage divider. Cheap simple and quick. A thermocouple is just a voltage input and that's what it simulates.

You could use a voltage divider to reduce the signal from the analog output. The analog output is 12 Bit and the range is +/- 10 VDC so the resolution it larger that what you would like for a thermocouple.

What are you trying to do???

Cheers,
Roger

I don't use the analog output at all. Simply a battery and voltage divider. Cheap simple and quick. A thermocouple is just a voltage input and that's what it simulates.

Ok, that's what I thought initially but wasn't sure.

You could use a voltage divider to reduce the signal from the analog output. The analog output is 12 Bit and the range is +/- 10 VDC so the resolution it larger that what you would like for a thermocouple.

Yes, I've thought about a voltage divider today, and I think the resolution will be sufficient. If I bring the 10V down to 10mV then the resolution should be 0.010mV, which is roughly 2 or 3 degrees for a type-R thermocouple.

What are you trying to do???

I'm trying to use type-N thermocouples, convert the temperature reading to a type-R voltage within the DT800, and then use the Ao to feed a furnace controller that is expecting type-R thermocouple input.

Given that I would need approx 4 m of type-R to do this, at $800/m, as opposed to about $20/m for type-N, a few resistors on a breadboard are very attractive! The ability to massage the temp data within the DT800 before passing it to the furnace controller is an added bonus.

Thinking about this a bit, some builtin functions for converting temperatures to various type thermocouple voltages (assuming an external voltage divider) would be a great feature for the next firmware update!

I hope that explains it

Cheers,
Chris.

Just a quick followup to this topic.

I pretty much have this working, using the Ao as a thermocouple simulator (albeit having to feed a voltage divider with a known gain). I needed to fit a 5th order polynomial to the standard 9th order curve that is specified for a type-R so that I could get around thermoelectric coefficients smaller than 1E-16.

Anyway, this process has turned the DT800 into a device that is unrivaled for flexibility and thermocouple type conversion ability, as far as Google tells me.

Cheers,
Chris