JBL M503 users

[Franks]

Hi,

The included pH probe is used and of unknown age and there is apparently a shelf life on them of around 2 years. I've seen some BNC pH sensors available on Amazon for around £20 which look identical to the JBL offering which is £75 and according to some of the reviews, there are happy JBL users using these instead of the official JBL variety. Can anyone vouch for this?

Thanks

 

[ian_m]

All home user affordable pH probes use the same method to measure pH, a glass sensing sphere membrane electrode full of a reference solution. Putting the electrode in a liquid solution produces a voltage across the membrane proportional to the pH of the solution it is dipped into. Fantastic, job done, CO2 level set...BUT...

However there are issues:

• The voltage is extremely tiny, typically 60mV per pH @ 25'C.
• The extremely tiny voltage depends on temperature. 54mV per pH at 0'C and 74mV per pH at 100'C. Better quality probes have a temperature sensor.
• Poorer quality cabling & connectors can generate many mV spurious voltages.
• Poorer quality electronics can't read the probes correctly, as well as a low voltage from probes is also extremely high impedance and require "clever" (& not cheap) electronics to read correctly. A suitable amplifier to read a pH probe (eg inductry standard LMP7721) is £5.50 each !!!
• Due to low voltages and voltage/current leakage from equipment in you tank will adversely affect readings. Many people experience different pH readings at each end of the tank. Possible fixes are locate pH probe in external pipe work, locate pH probe in earthed pipe/container.
• pH probes need regular calibration as the solution in the membrane degrades/dilutes/changes over time affecting the readings.

Personally I have used a drop checker, just slowly dialing up CO2 until the drop checker is nicely green at lights on.

 

[Franks]

Cheers for your input Ian.
The M503 kit includes a touch interface computer with various inputs to help mitigate some of these issues I guess. One of them being a separate temperature probe.
I might bite the bullet and give the Amazon pH probe a go. The JBL probe has around 6 months of use on it but it could have been on the shelf in a shop for a year before that. It's also dried out completely but might be revived by soaking in distilled water and recalibrated by the computer and some reliable pH buffer solution.

Thanks again.

 

[blairgerman]

Never tried the off brand cuz surely the poor quality will affect the readings for the reasons @ian_m mentioned. These Milwaukee ones have been great, but i can't find them on the UK amazon - i do see the BLUELAB ones there which I've had good luck with but they're closer in price to the ones that came with your kit. The reference and storage solution have helped me a lot - Never let them sit dry.

 

[sh4d0w]

DId you try the cheaper probe?

 

[Franks]

Not yet. I will be getting a replacement probe soon so will let you know. I've been busy building a cabinet for my Scaper600. I will try and rejuvenate the JBL probe with distilled water too. Will keep you posted.

 

[Franks]

I've ordered a cheap eBay one for £11. I'll let you know how it pans out 👍🏼