PTSA probes read in parts per billion — an extremely precise measurement of trace chemical. When one is not tracking its set point, work through these checks in order: the signal, the installation, the probe, then the controller’s calibration.
Compare like with like. When checking an inline probe against a handheld, use a handheld from the same manufacturer as the probe. Manufacturers calculate the value with different technologies, and differences in turbidity and color make their readings disagree widely.
On the MicroVision EX, scroll down the home screen to the PPB reading. The line beneath it shows the probe’s raw analog signal.
PTSA probes store their own diagnostic and calibration data, which the manufacturer’s tools can read.
For the Pyxis ST-500, use the Pyxis MA-WB — an inline Bluetooth device that checks the probe’s cleanliness and adjusts its calibration through the uPyxis app. See Pyxis’s video on cleaning and calibrating the probe.
Turner Designs also makes tools for its probes.
The MicroVision EX accepts many kinds of 4–20 mA probe. Calibrate it for the PTSA probe manually, or import a known calibration.
Set the units to PPB, then run a two-point calibration, with at least 2 mA between the two points:
With about 100 PPB of product in the system, the default scale should give about 12 mA. If it doesn’t, the probe is probably still fouled.
For a new or known-clean probe, import the factory-default PTSA configuration for 4–20 mA input 1 — see Configuring a PTSA Probe.