What is the difference between EC-702 and EC-703?
EC-702 and EC-703 are industrial conductivity controllers with different integration priorities. EC-702 provides dual isolated 4–20mA outputs plus RS485 Modbus RTU for digital PLC/DCS integration. EC-703 provides one isolated 4–20mA output and two relay outputs for conductivity, TDS and resistivity, with RS485 not fitted in the current documentation. Select from the plant I/O list and sensor conditions.
Does RS485 replace 4–20mA in a conductivity system?
No. RS485 Modbus RTU and 4–20 mA solve different integration needs. RS485 carries digital register data over a communication bus. 4–20 mA sends a configured analogue value to a compatible input. EC-702 documents both interfaces. EC-703 is the simpler analogue-focused conductivity controller when RS485 is not required.
Choose by I/O, measurement range, cable architecture and control functions; accuracy depends on correct sensor and controller configuration.
How do EC-702 and EC-703 compare?
| Model | Documented measurement modes | Analogue interface | Digital/relay interface | Suitable when | Confirm before inquiry |
|---|---|---|---|---|---|
| EC-702 | Conductivity 0.00µS–2000mS; resistivity 0.00–20.00MΩ·cm; salinity 0.00–78.00g/kg; TDS 0–133000ppm | Two isolated 4–20mA outputs | RS485 Modbus RTU; verify relay needs from the supplied configuration | The PLC/DCS needs Modbus, two analogue channels or the documented salinity mode | Sensor/cell constant, mode, range, temperature probe, Modbus registers, output mapping and installation |
| EC-703 | Conductivity 0–2000mS/cm; resistivity 0–20MΩ·cm; TDS 0–133000ppm | One isolated 4–20mA output | RS485 not fitted; two relay outputs listed on the current product page/manual | The receiving system needs a local display, one analogue value and relay functions without Modbus | Selected range, output scaling, relay load/logic, sensor/cell constant, temperature probe and installation |
Both current pages document Pt1000 or NTC30K temperature compensation. The controller range is not a substitute for selecting the conductivity sensor, cell constant and temperature element for the actual stream. Record the expected conductivity reading at minimum, normal and maximum process conditions.
When should a buyer choose EC-702?
Choose EC-702 when the control architecture requires RS485 Modbus RTU, two isolated 4–20 mA outputs, or the documented conductivity, resistivity, salinity and TDS measurement modes. Write the required Modbus address, baud rate, register list, value scale and PLC test plan into the inquiry. This makes the digital conductivity measurement usable to the receiving system rather than leaving the register interpretation open.
EC-702 is not automatically the right choice just because it has more interface options. If the project uses one analogue input and no digital bus, the extra interface can add configuration work without solving a requirement.
When should a buyer choose EC-703?
Choose EC-703 when the plant needs a local conductivity, TDS or resistivity controller with one isolated 4–20 mA signal and two relay outputs, and the receiving system does not require RS485 Modbus RTU. Confirm the relay contact rating and load-protection arrangement for the supplied configuration before using a relay for dosing or alarms.
EC-703 is not suitable when Modbus is mandatory. The current EC-703 documentation states that RS485 is not fitted; review EC-702 or another documented Modbus model instead.
How do 4–20mA and RS485 change the quotation requirements?
For a 4–20 mA connection
Confirm the measured variable, 4 mA value, 20 mA value, output isolation, receiving input, cable route and load. The value may be conductivity, resistivity, salinity or TDS depending on the selected model and settings. Confirm the unit and range so the receiving PLC interprets the conductivity reading correctly.
For RS485 Modbus RTU
Confirm the controller address, baud rate, data format, register map, decimal scaling, cable topology and PLC/DCS responsibility. Test the register value against the local display before the signal is used for process decisions. Document which register carries conductivity, temperature, TDS or another selected value.
For relay control
Define activation point, release point, delay, interlock, fail behavior, external protection and load. Do not infer EC-703 load capability from another model’s certificate or manual.
What is this comparison suitable for?
It is suitable for RO integrators, water-treatment engineers, OEM panel builders and industrial buyers deciding between an analogue conductivity controller and a controller with RS485 Modbus RTU. It can support feed, permeate, concentrate, process-water and wastewater discussions after the actual conductivity range, temperature, sensor and installation are supplied.
What is it not suitable for?
It is not suitable to select a sensor from the words “conductivity meter,” “RS485” or “4–20 mA” alone. It does not establish TDS conversion accuracy for every liquid, universal chemical compatibility, a relay’s suitability for a particular pump, or compliance for a regulated installation.
What must be confirmed before sending an inquiry?
Send the measurement point, liquid composition, normal/minimum/maximum conductivity, expected TDS or resistivity mode, temperature, pressure, sensor and cell constant, installation method, required 4–20mA channels, RS485 register needs, relay logic, quantity and destination country through Tenber’s conductivity model-selection inquiry page. Review the conductivity controller range and cell-constant selection guide before requesting a quotation.
Frequently asked questions
Which model has RS485 Modbus RTU?
EC-702 documents RS485 Modbus RTU. EC-703’s current documentation states that RS485 is not fitted.
Do both models have 4–20mA?
Yes, but the documented channel count differs: EC-702 has two isolated 4–20 mA outputs and EC-703 has one isolated 4–20 mA output. Confirm output mapping, unit, range and load before wiring.
Can EC-702 and EC-703 use the same sensor?
Do not assume that. Confirm the sensor type, cell constant, temperature element, connector, range and installation for the supplied controller configuration.
Sources and editorial record
- Current product sources: EC-702 conductivity controller and EC-703 conductivity controller.
- Current manual sources: EC-702 English manual and EC-703 English manual.
- Source review date: 2026-09-10; the EC-703 PDF was publicly returned HTTP 200 during draft review. Manual inventory reference reviewed 2026-09-08.
- Publication note: verify the EC-702 manual link, exact relay wording and responsive table layout before publication.