Hello all,

I have one of these

http://www.omega.co.uk/ppt/pptsc.asp?ref=CDTX300

This is within a big adaptable box and I need to move the 4 x trimmers so the user can insert a small screwdriver into the side of the big adaptable box and turn them

I have taken the unit apart (see below pics)

The length I need to extend these is around 300mm

According to the spec sheet
http://www.bourns.com/pdfs/3296.pdf

one is 200 ohms
and the other three are 50K ohms

Due to these working on resistance if I were to get 4 x 300mm lengths of 3 core screened cable, desolder them and move them do you think it is possible? In theory they are easy to mount on the inside of the big adaptable box as all I would need to do is drill 4 x holes into it and possibly glue them in place so the user just pushes in a screwdriver and turns them.......

 

You can replace the trimpots with ones that can be mounted on the front panel with the proper holder:

trimpots:

http://www.digikey.com/product-detail/en/3005P-1-201/3005P-201-ND/83356

http://www.digikey.com/product-detail/en/3005P-1-503/3005P-1-503-ND/2534616


trimpot front panel mount holder:

http://www.digikey.com/product-detail/en/H-83P/H-83P-ND/388693

 

Thanks...so as far as extending them there shouldnt be an issue with resistance and/or noise?

What kind of cable would you recommend?

You can replace the trimpots with ones that can be mounted on the front panel with the proper holder:

trimpots:

http://www.digikey.com/product-detail/en/3005P-1-201/3005P-201-ND/83356

http://www.digikey.com/product-detail/en/3005P-1-503/3005P-1-503-ND/2534616


trimpot front panel mount holder:

http://www.digikey.com/product-detail/en/H-83P/H-83P-ND/388693

 

That kind of depends on what signals are going through those trimpots. If it is just DC or low frequency then you should be ok, but anything faster will probably have problems with the capacitance and inductance of those 30cm wires. Another factor will be interference induced into those wires, which might be problem as well.
So I guess you will have to try and see what works.

 

As kubeek says, a lot depends on the application and circuit details.
Do you know what part of the circuit or what parameters the trimpots are adjusting?
Are these gain or zero adjustments?

Start off with the shortest wires possible. If that causes a problem you can switch to shielded cables.

 

Thanks for the replies...

The 4 pots are as follows

PH 7 pot..you put the ph probe into ph 7.0 calibration solution and adjust it so it reads 12.00 mA

PH 4.0 pot..you put the ph probe into ph 4.0 calibration solution and adjust it so it reads 8.57mA

Conductivity offset pot..you leave the conductivity probe so it is dry and in free air and adjust until it reads 4.00mA

Conductivity slope pot..you put the conductivity probe into 5.00 mS/cm calibration solution and adjust until it reads 12.00mA

 

The resistance of your wire will only be a fraction of an ohm so your trimmers can be adjusted to account for that. pH meters are DC creatures so the biggest problem you will have is interference from other devices causing offset or drift in your measurements. On a 50k ohm device, interference from AC devices nearby shouldn't be too noticeable.

 

The resistance of your wire will only be a fraction of an ohm so your trimmers can be adjusted to account for that. pH meters are DC creatures so the biggest problem you will have is interference from other devices causing offset or drift in your measurements. On a 50k ohm device, interference from AC devices nearby shouldn't be too noticeable.

What about the 200 ohm resistor?

 

Agreed. You should be fine.

 

What about the 200 ohm resistor?

50,000 ohm was a range for discussion. 50200 ohm falls into that range.