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Author Topic: Using pokeys56e a2d to measure voltages - accuracy and protection  (Read 4223 times)

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I have just bought a pokeys56e to do some monitoring jobs on our small boat.

Specifically I am going to use it to measure some battery voltages.

Does anyone know how accurate the voltage reference on the pokeys56 is?  I don't need absolute accuracy as I can of course calibrate the measurement myself (and will have to use a voltage divider anyway as I'm measuring more than 3.3 volts) but I do need the voltage reference to be stable within 1% or so.

Secondly what sort of protection should I provide for the inputs, is there a standard way to do it.  The boat electrical environment is fairly noisy (essentially much like a car).

Offline NeoTO

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Re: Using pokeys56e a2d to measure voltages - accuracy and protection
« Reply #1 on: November 02, 2012, 03:32:54 AM »
The voltage reference is present in the low-drop voltage regulator on the board, which is LD1117 (datasheet says that its temperature stability is typically around 0.5%, while it should be generally 1% accurate at 25 °C and 2% in all temperature range).

Regarding the protection - I would suggest a zener or suppressor diode between voltage divider and PoKeys, and a small choke would make it even better.
However, you should pay attention also to the power supply - suppressor and choke are mandatory here.
Generally, anything that goes in or out of PoKeys (except the network cable) must be protected by suppressor (or zener).
www.poscope.com home of PoKeys USB HID, IO, USB, Ethernet controler and PoScope USB PC oscilloscope
Re: Using pokeys56e a2d to measure voltages - accuracy and protection
« Reply #2 on: November 02, 2012, 04:47:39 AM »
OK, thanks, that's just the sort of advice/information I was after.
Re: Using pokeys56e a2d to measure voltages - accuracy and protection
« Reply #3 on: November 02, 2012, 10:11:31 AM »
I have never read anything from pokeys about suppressor diodes or zeners on every  line, can you provide a little more info, part numbers, etc ?

Offline NeoTO

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Re: Using pokeys56e a2d to measure voltages - accuracy and protection
« Reply #4 on: November 02, 2012, 12:40:20 PM »
This information will be included in the PoKeys manual in two weeks time.
Generally, it is preferred to include protection of power and signal inputs and outputs in noisy environments.
www.poscope.com home of PoKeys USB HID, IO, USB, Ethernet controler and PoScope USB PC oscilloscope

Offline NeoTO

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Re: Using pokeys56e a2d to measure voltages - accuracy and protection
« Reply #5 on: November 20, 2012, 10:45:14 AM »
Here is the circuitry that can be used to protect the PoKeys inputs if the device is used in (electrically) noise environments.
www.poscope.com home of PoKeys USB HID, IO, USB, Ethernet controler and PoScope USB PC oscilloscope