I am attempting to measure the potential from a pH probe connected to the analog input channel (1*V). The pH probe is calibrated with known buffer solutions:
• pH 7: 0 mV
• pH 4: 175 mV
While the probe outputs the expected values when measured directly using a voltmeter (with the DT85 offline), the readings become completely unstable and random when the DT85 is active and taking measurements.
I have also tried the following troubleshooting steps:

1. Changed the input channel to others (e.g., 1V, 2V) without success.
2. Verified the probe output at the DT85 terminals using a voltmeter, which reads correctly when the logger is offline. However, the voltmeter also shows incorrect and fluctuating values when the DT85 is turned on.
3. Ensured the probe is in good condition and outputs stable readings when connected to a standard pH meter.
4. Verified that other sensors (ORP and RTD probes) connected to the logger are working as expected, with stable and accurate readings.

Setup Information:
• Logger Model: DataTaker DT85
• Probes in Use: pH probe, ORP probe (working fine), and RTD temperature probe (working fine).
• pH and ORP probes are connected in a PHTX-22 Preamplifier

Request for Assistance:
Could you please advise on:

1. Any additional settings or configuration changes required to ensure stable readings from the pH probe?
2. Whether the issue could be related to input impedance or noise interference, and how to mitigate these?
3. If an external amplifier or buffer might be necessary for compatibility with the DT85?

Hi adalberto,

We have reach you via the email, there are a couple of information that we need to get a better understanding about your system.

• What is the observable offset between the measurement and voltmeter?
• Can you share the wiring detail and a copy of your program? (You can respond to our email rather than posting it in the forum if the program contain a sensitive information).

Best regards,
dataTaker Expert