Key Technical Specifications
- Product Model: 871EC-SP0
- Manufacturer: Foxboro / Schneider Electric
- Measurement Principle: Inductive (Toroidal / Electrodeless)
- Sensor Type: Conductivity Probe
- Protection Rating: IP68 (Fully submersible)
- Compatible Analyzers: 875EC, 873EC, 873AEC, 870ITEC, 870EC
- Wetted Materials: PEEK, PFA, CPVC (Verify specific suffix)
- Process Connection: Varies by suffix (Flange, Threaded, Retractible)
- Signal Output: Inductive current proportional to conductivity
- Design Feature: Encapsulated dual-coil assembly
Product Introduction
Sludge, grease, and coating buildup will absolutely destroy a traditional contact conductivity cell in a matter of weeks. I’ve walked into plants where operators were pulling sensors out of the line every single shift just to scrub them clean. The Foxboro 871EC-SP0 exists specifically to stop that madness. Instead of bare metal electrodes, it uses two encapsulated toroidal coils inside a plastic housing. One coil excites the liquid, and the other reads the resulting current loop. No metal touches the fluid, so there is nothing for the gunk to stick to.Engineers keep specifying this specific 871EC-SP0 model because it actually survives in wastewater and chemical slurry applications where standard cells fail. It pairs directly with the 875EC Intelligent Analyzer or the 870ITEC transmitter. Just be careful with the suffix. The ‘SP0’ designation dictates your wetted materials and process connection. I’ve seen guys order this exact base model only to find out their pipe thread didn’t match. Always double-check the full tag before you buy.
Quality SOP & Tech Pitfalls
Before this 871EC-SP0 leaves our bench, it goes through a strict protocol. We start with a visual and counterfeit check under magnification to ensure the PEEK/PFA housing isn’t cracked or chemically etched. Next, it goes on a live test rack with an 875EC analyzer to verify the inductive loop generates the correct 4-20mA signal across the range. We then perform an insulation resistance check with a Fluke 115 to guarantee the internal coils aren’t shorted to ground. Finally, we log the firmware/hardware revision and seal it in anti-static packaging.Here is where people mess up: Do not use a megohmmeter (megger) on the sensor cable. The high voltage will instantly fry the internal toroidal coils. I watched a tech ruin a brand new 871EC-SP0 because he treated it like a standard motor cable. Also, check the O-ring. If the old O-ring is flattened or nicked, do not reuse it. A bad seal lets process fluid into the cable conduit, and that sensor is dead. Take a picture of the old wiring before you pull it.
Installation & Configuration Guide
- Pre-Installation: ⚠️ Lockout/Tagout the 875EC analyzer power. Verify the process line is drained and depressurized. Take a clear photo of the existing sensor wiring and the mounting hardware.
- Removal: Label the three or four sensor wires. Unscrew the conduit fitting and loosen the process coupling. Carefully pull the old 871EC-SP0 out of the fitting or retraction housing. Inspect the threads for corrosion.
- Installation: CRITICAL: Verify the new 871EC-SP0 has the exact same process connection and wetted materials as the old unit. Apply fresh lubricant to the O-ring. Thread the sensor in hand-tight, then use a strap wrench if needed. Never overtighten the plastic housing.
- Power-On & Testing: Reconnect the wires exactly as photographed. Restore 24V DC power to the 875EC analyzer. Watch the LED boot sequence. Navigate the analyzer menu to verify the sensor type is recognized and the raw conductivity reading is stable before returning the line to service.
Compatible Replacement Models
| Replacement Model | Compatibility Tier | Field Notes |
|---|---|---|
| 871EC-SP0-3V | ✅ Drop-in Replacement | Exact match. The -3V just denotes a specific cable length or revision. Safe to swap. |
| 871EC-PP0-4 | ⚠️ Software Compatible | Same toroidal tech, but different wetted materials (PP). Requires verifying chemical compatibility with your process fluid. |
| 871EC-TF2-3V | ⚠️ Software Compatible | Different process connection (TF). Will physically fit the analyzer, but requires changing the pipe fitting. Labor time: ~1 hour. |
Frequently Asked Questions (FAQ)
Can I hot-swap this sensor without shutting down the analyzer?
No. The 875EC analyzer expects a specific inductive signature. Pulling the 871EC-SP0 while powered can cause the analyzer to fault or output a false high-range alarm. Always kill the power first.Why is my reading drifting wildly after installation?
You likely have air trapped in the toroidal donut. The 871EC-SP0 needs to be fully submerged and purged of air bubbles to form a complete inductive loop. Tap the housing gently or adjust the flow rate to bleed the air out.Is this the same as a standard 4-20mA transmitter?
No. The 871EC-SP0 is a passive sensor. It does not output 4-20mA on its own. It relies entirely on the 875EC or 870ITEC to excite the primary coil and measure the secondary current. Don’t wire it to a generic PLC analog input.Can I use generic replacement O-rings?
I wouldn’t risk it. Process fluids eat standard Buna-N for breakfast. Use only Foxboro-specified O-ring kits for the 871EC-SP0 to prevent chemical degradation and subsequent leaks into the electronics compartment.How do I clean this thing if it does get coated?
Even though it’s electrodeless, heavy wax or scale can block the inductive field. Pull it and soak it in a mild acid or solvent compatible with the PEEK/PFA housing. Never use abrasive pads or wire brushes on the plastic body.What happens if the cable gets cut and spliced?
Don’t splice it. The toroidal signal is highly sensitive to cable capacitance and shielding. A field splice will introduce noise and ruin your calibration. If the cable is damaged, replace the entire 871EC-SP0 sensor assembly.
