YSI EXO

EXO Smart Sensors are interchangeable digital sensors that plug into any port, retain their own calibration, and work on every EXO sonde. The model sets only how many sensors run at once and whether a central anti-fouling wiper fits: EXO1/EXO1S have 4 ports (no central wiper), EXO3/EXO3S have 5 ports, and EXO2/EXO2S have 7 ports. So every model can measure the full parameter suite; the smaller sondes simply measure fewer parameters simultaneously.

The S-series (EXO1S, EXO2S, EXO3S) is mechanically the same as EXO1/EXO2/EXO3 with identical ports and sensor support, but omits the internal D-cell battery compartment, so it is shorter and lighter and must be powered externally (handheld display, KorLink, or a data logger). Use the battery models for autonomous logging and the S-series for externally-powered continuous monitoring or spot sampling.

The EXO Central Wiper clears biofouling, sediment, and debris from the sensor faces during long deployments. It occupies the center port and can be fitted to the EXO2, EXO2S, EXO3, and EXO3S. It is not compatible with the EXO1 or EXO1S, which have no central port; those sondes rely on copper anti-fouling accessories (copper tape, C/T screen, guards, sleeves) instead.

Many EXO sensors output derived parameters alongside their primary reading. For example, the Conductivity/Temperature sensor yields temperature, conductivity, specific conductance, salinity, and total dissolved solids. The optical dissolved-oxygen sensor adds a local %-saturation reading, and turbidity derives total suspended solids. The Total Algae sensor pairs chlorophyll with either phycocyanin (TAL-PC) or phycoerythrin (TAL-PE), and the Ammonium ISE derives un-ionized ammonia (NH3) when a pH sensor is present.

Depth is measured by a non-vented pressure transducer built into the sonde body and does not occupy a sensor port. Pick the 10 m, 100 m, or 250 m range to match the deployment. The transducer's raw reading is reported as absolute pressure (psia/psig) and the sonde computes depth/level from it, so both a water-pressure and a water-level parameter are available. Nitrate, meanwhile, can be measured either by ion-selective electrode or by the NitraLED optical UV sensor; both report nitrate.

The driver connects to the EXO serial output (9600 baud, 8-N-1) through a Signal Output Adapter: the DCP SOA for SDI-12/RS-232 or the Modbus SOA for RS-485. The EXO3/EXO3S provide native SDI-12, so they need no DCP SOA. It reads the sonde's serial number and firmware, then asks the sonde which parameters it is configured to output and logs those values each interval. The integration therefore ingests exactly the sensors installed and enabled on the sonde, so the parameter template set in KOR software controls what is recorded.

The driver polls the sonde over SDI-12 (1200 baud, 7-E-1) with the standard 'M' measurement command. The SDI-12 response is a bare, positional list of floating-point values with no per-value labels; the sonde does not send a header naming each reading. The integration therefore ingests the values as ordered channels and the meaning of each channel is fixed by the sonde's own configured sensor/parameter order, set in YSI's software (EcoWatch/6-Series) when the sonde is prepared. This page lists the full set of quantities a 6-Series sonde can report; a given deployment outputs only the sensors installed and enabled on that sonde.

It depends on the number of optical ports. The 6820 V2-1 and 6920 V2-1 accept a single optical sensor; the 6600 V2-2, 6600EDS V2-2, 6820 V2-2, and 6920 V2-2 accept two; and the 6600 V2-4 accepts four. The optical family is turbidity, chlorophyll, rhodamine WT, blue-green algae PC, blue-green algae PE, and optical (ROX) dissolved oxygen, so the port count sets how many of these run simultaneously. The wet-chemistry electrodes (pH, ORP, conductivity, the nitrate/ammonium/chloride ISEs) and the depth transducer occupy their own dedicated ports.

6-Series sondes offer two DO technologies: the 6562 Rapid Pulse polarographic sensor and the 6150 ROX optical sensor. Both report dissolved oxygen as % air saturation and as mg/L; the optical ROX resists flow dependence and fouling for long deployments, while Rapid Pulse suits shorter or profiling work. On Aethair, both map to the single Dissolved Oxygen parameter.

No. YSI discontinued the 6-Series. Final sales ended between 2017 and 2018, and factory support ended in 2022–2023. It is superseded by the EXO platform (EXO1/EXO2/EXO3), which uses interchangeable smart sensors. The 6-Series remains in service in many long-running monitoring networks, which is why the driver is still maintained.

The sonde carries a pressure transducer (vented on the 600LS 'level' sonde, non-vented on the others). Its raw reading is reported as absolute or gauge pressure (psia/psig), and the sonde derives depth or level in meters or feet from it, so both water-pressure and water-level parameters are available from one transducer.