The AZ Instrument 8685 is a pocket pH pen reading pH 0–14 to ±0.2 with water temperature on the same screen and automatic temperature compensation (ATC). It calibrates at up to three points, holds a reading at the press of a button, and is housed to IP65. AZ Instrument is a Taiwanese manufacturer of water quality and environmental meters. Stocked in Sydney and shipped domestically.
A simple, dependable pH pen
The large LCD shows pH and temperature together, a stability indicator tells you when the reading has settled, and data hold freezes the number so you can lift the pen out and read it. ATC corrects the pH reading for water temperature automatically, which matters in a reservoir that warms and cools through the day. Calibration values are adjustable, it switches between °C and °F, and it powers itself off to save the batteries.
At ±0.2 it is built for keeping a solution in range rather than lab work. For tighter accuracy or a replaceable probe, see the AC Infinity pH Meter PRO Kit (±0.01).
Keep the electrode wet
The pH electrode is protected by a cap designed to keep the glass bulb wet between uses. AZ rate the sensor life at more than 6 months with good maintenance, and storage is what decides it: cap on with a little storage or pH 4 solution inside, rinse in clean water before the next test, and never let it dry out.
Where it gets used
Nutrient reservoirs and run-off, feed water, aquariums and ponds, pools and spas, and general water treatment. Pair it with the AZ 8362 EC & TDS Pen to cover nutrient strength as well as pH.
Specifications
| Product identification | |
| Manufacturer | AZ Instrument Corp. |
| Model | 8685 |
| Performance and technical | |
| pH range | 0.0–14.0 |
| pH accuracy / resolution | ±0.2 / 0.1 |
| Temperature range | 0–60 °C |
| Temperature accuracy / resolution | ±1 °C / 0.5 °C |
| Temperature compensation | Automatic (ATC) |
| Calibration | Up to 3 points (pH 4 / 7 / 10; USA, NIST or DIN buffers) |
| Ingress rating | IP65 |
| Sensor life | More than 6 months with good maintenance (manufacturer rating) |
| Operating conditions | 0–50 °C, under 80% RH |
| Battery | 4 × LR44 (included) |
| Functions | Data hold, stability indicator, low battery indicator, auto power off, °C/°F |
| Dimensions | 165 × 35 × 32 mm (6.5 × 1.4 × 1.3 in) |
| In the box | Meter, batteries, manual |
| Documentation | |
| Operation manual | 8685 operation manual (PDF) |
| Specification sheet | 8685 specification (PDF) |
| Certification | CE certificate (PDF) |
FAQ
Is ±0.2 accurate enough for hydroponics?
For keeping a nutrient solution inside its target range, yes, provided it is calibrated regularly. If you want to see small day-to-day drift, a ±0.01 pen such as the AC Infinity pH Meter PRO Kit shows it earlier.
Does it read EC or PPM?
No, pH and temperature only. For EC and TDS, add the AZ 8362 EC & TDS Pen, or choose the AC Infinity Hydroponic Meter PRO Kit for everything in one pen.
Can I replace the electrode?
No, the electrode is part of the pen. Good storage is what keeps it going; see the section above.
Is IP65 fully waterproof?
IP65 is protected against dust and water jets, so splashes and a wet bench are fine. It is not rated for being dropped in and left under water; fish it out and dry the body if that happens.
How often should I calibrate?
Before first use, then about monthly with regular use, and any time a reading looks wrong. Use fresh buffer each time rather than pouring used solution back.