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Guide to measure conductivity

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Guide to measure conductivity

Postby Shiv » Sun Feb 08, 2015 1:12 am

Good day,

Is it possible to use DrDaq to measure conductivity?
What voltage sensors and signal processors would I need to purchase to achieve this?

Thanks,
Shiv
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Re: Guide to measure conductivity

Postby Hitesh » Thu Feb 19, 2015 12:25 pm

Hi Shiv,

The USB DrDAQ has a resistance input so you might be able to use that.

You can view the specifications for the Resistance input via the link below:

https://www.picotech.com/data-logger/drdaq/drdaq-specifications

You would have to configure your own circuit but I am unable to advise on this.

Regards,
Hitesh

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Re: Guide to measure conductivity

Postby Glovisol » Thu Feb 19, 2015 1:17 pm

Hi Shiv,

The DrDAQ, with the last version of PICOLOG, VERSION r5_24_2, can measure resistance in the range 1kOHm - 1 MOhm with 0.5% precision, once the ad hoc corrections have been put in place. See "Problems with resistance measurement of the USB DrDAQ" in the USB DrDAQ Forum. So, in principle this unit can also measure resistivity. However please state resistivity of WHICH you need to measure: is that of an electrolytic cell or of a bar of material, or what? Also what is the resistivity RANGE you need?
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Re: Guide to measure conductivity

Postby Glovisol » Sat Feb 21, 2015 9:31 am

Hi Shiv,

The DrDAQ can indeed be used for conductivity measurements by using the 3 available EXT. channels as data acquisition in Picolog, plus the Resistance channel as an overall check.

EXT. 1 CHANNEL logs sample temperature measured with an LM35, or other miniature sensor.
EXT. 2 CHANNEL logs voltage.
EXT. 3 CHANNEL logs current value coming from a standard current probe (Pico) or high precision commercial Hall Effect sensor.
RESISTANCE CHANNEL logs resistance independently, as an overall control, within the limitations described below.

A fixed voltage (AC or DC, depending on material and status, liquid, solid, jelly, etc. to be measured) is applied to the sample and current flows. This power will increase the temperature of the sample. The DrDAQ will record all 4 quantities in PICOLOG. Resistance at any different temperature is calculated by the PICOLOG's math channel by Ohm's law. Then the standard Conductivity equation, knowing area and length, is used in another math channel to calculate Conductivity. Picolog will then automatically graph Conductivity Vs. Temperature. In between the applied voltage is switched off at various temperatures and the resistance channel, connected via a switch, records raw resistance at any desired temperature as an overall check. This resistance can then be converted to conductivity by applying the standard equation and this result used for comparison. Due to the lower limit of the Resistance channel (1 KOhm) this channel could not be used depending on the measurement range needed. Therefore an automated electrical conductivity measurement system is possible within the DrDAQ/PICOLOG capabilities.

In synthesis you need:

- DrDAQ + PICOLOG software.
- Suitable AC Variac or adjustable DC Supply.
- Standard current probe/current sensor.
- LM35 type temperature probe or any other miniature probe.
- Special fixtures for the application of current flow/temperature measurement. This depends on what kind of material the measurement has to be taken.

This method and the DrDAQ would be especially useful if you needed to collect data as control in a continous process: the DrDAQ would record and display Conductivity and Temperature for an undefinite time period.
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Re: Guide to measure conductivity

Postby JonWood » Sun Oct 18, 2015 6:52 pm

I have a similar question. I'm wanting to record a Galvanic Skin Response (GSR), which is usually only a couple of micro-siemens range in peak to peak. The specification suggests that this may be too small a range for the DrDAQ to measure. Do you have any suggestions about the bast way that i can make this work with the hardware and datalogger?
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Re: Guide to measure conductivity

Postby Gerry » Fri Oct 23, 2015 8:26 am

Hi John,

Purely for reference, a good way to measure small changes in resistance would be to use a wheatstone bridge.

However, Pico Technology strongly advises against the use of any of our products where the application involves direct contact with the body. There are strict standards applicable to these types of applications (e.g. under US legislation there is UL544 along with other recommendations and requirements) and our products have NOT been designed to meet these standards.

Regards,

Gerry
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Re: Guide to measure conductivity

Postby Gerry » Fri Oct 23, 2015 8:33 am

Hi John,

Sorry the standards applicable are UL60601-1 which replaced UL544.
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