SI-100 Rigid Probe Magnetostrictive Level Transmitter
Stainless probe, 0.2 to 6 m measuring range, ±0.1 mm accuracy, 4-20 mA / HART / Modbus, ATEX option. Built for atmospheric and pressurized tanks where you need a rigid stem instead of a flexible cable.
- Range: 0.2-6 m rigid. Up to 23 m with flexible cable variant.
- Accuracy: ±0.1 mm or 0.05 % of FS, whichever is greater.
- Output: 4-20 mA + HART, RS-485 Modbus RTU, or 0-10 V.
- Process: -40 to +125 °C standard, +200 °C with extension. PN16/PN40 flange or 1″ NPT.
- Certifications: ATEX/IECEx Ex ia IIC T6 Ga (Zone 0 capable). IP67.
Why Engineers Spec the SI-100
Four reasons it gets picked over float, ultrasonic, or guided-wave radar in our daily quote requests.
±0.1 mm
Repeatable AccuracyBetter than float by ~50× and better than 4-20 mA radar by ~10× for tanks under 6 m.
No Drift
Time-of-Flight ReadingThe torsional pulse on the waveguide does not drift with temperature, dielectric, or coating.
2 Outputs
4-20 mA HART + ModbusDrops into a PLC analog input or a Modbus poll loop without buying a new transmitter.
ATEX Ex ia
Zone 0 CapableSame body as the standard model; just add the safety barrier on the cabinet side.
Full Specification Sheet
What you will see on the line item of the quote. Download the PDF datasheet from the request form below.
| Item | SI-100 Standard | SI-100 Ex (ATEX/IECEx) |
|---|---|---|
| Probe type | Rigid stainless rod, 316L | Rigid stainless rod, 316L |
| Measuring range | 0.2 m – 6 m | 0.2 m – 6 m |
| Resolution | 0.01 mm | 0.01 mm |
| Linearity | ±0.05 % FS or ±0.1 mm (greater) | ±0.05 % FS or ±0.1 mm (greater) |
| Repeatability | ±0.005 % FS | ±0.005 % FS |
| Output | 4-20 mA / HART / Modbus RTU / 0-10 V | 4-20 mA + HART (Ex ia) / RS-485 (Ex ia) |
| Power supply | 24 VDC ±10 % | 24 VDC via Ex ia barrier |
| Process temperature | -40 to +125 °C (+200 °C with extension) | -40 to +85 °C (T6) / -40 to +120 °C (T5) |
| Process pressure | 0 – 4 MPa (40 bar) | 0 – 4 MPa (40 bar) |
| Process connection | 1″ NPT / G1″ / DN50 PN16 / DN50 PN40 flange | Same as standard |
| Float (included) | SUS304 ring float, 50 mm OD, ≥ 0.6 g/cm³ | SUS304 ring float with Ex cable gland |
| Housing | Aluminum die-cast, IP67 | Aluminum die-cast, IP67 |
| Cable entry | M20 × 1.5 | M20 × 1.5 with Ex cable gland |
| Hazardous area | Safe area only | Ex ia IIC T6…T4 Ga (Zone 0) |
| Approvals | CE, RoHS | CE, RoHS, ATEX, IECEx |
How Magnetostriction Actually Measures Level
- The transmitter head fires a low-current interrogation pulse down a tensioned waveguide wire inside the rigid stem.
- A donut float wrapped around the stem carries a permanent magnet. Where the pulse meets the magnetic field, the wire twists slightly — that twist is a torsional pulse.
- The torsional pulse travels back up the waveguide at ~2,830 m/s. The transmitter clocks the round-trip time.
- Distance = ½ × travel time × wave speed. A 1 GHz timer gives 0.01 mm resolution.
Why it matters in the field: no capacitance plate to coat, no ultrasonic beam to scatter on foam, no microwave dielectric to fight. The pulse is mechanical and the trigger is magnetic, so dirty liquids, vapors, and dielectric changes do not affect the reading.
Where the SI-100 Fits (and Where It Doesn’t)
The rigid-stem version owns four common tank shapes. If your tank looks like one of these and the depth is under 6 metres, the SI-100 is a one-line BOM addition.
Ceiling / Suspended Tanks
Top-mount through a flange. Probe length picked to leave 50 mm dead zone at the bottom. Common in chemical dosing rooms.
Buried Fuel Tanks
Diesel, petrol, or AdBlue. 4-20 mA + HART output feeds station controllers. Choose Ex ia version for petrol.
Small Process Containers
Day tanks, mixing vessels, lube reservoirs. Short probe (300-800 mm) keeps the float stable in narrow geometry.
Agitated / Foaming Tanks
Use the external stilling-well variant. The float sits inside a side chamber so the agitator does not whip it around.
Three Ways to Mount It
Tell us which one fits your tank when you request the quote and we will ship the right adapter pre-fitted.
1. Top Mount (Thread or Flange)
Default option. 1″ NPT, G1″, or DN50 PN16/PN40. Probe drops straight down through the tank top.
2. Positioning Ring
For tanks where you cannot drill a flange. A clamping ring holds the rigid stem at the top opening.
3. External Stilling Well
Side-mounted chamber connected by upper and lower process taps. Used for agitated, foamy, or coating liquids.
Sizing the Probe Length
The probe is cut to order. Get this wrong and you either lose dead-band at the top or pay for steel you do not need. Three numbers go on the quote:
- H1 — Top Dead Zone: 50 mm minimum from the flange face down to the highest reading point. Add the height of the top fitting (a DN50 flange eats 30-60 mm).
- H2 — Live Measuring Length: the distance you actually want to read. Make this the working range you care about, not the full tank height.
- H3 — Bottom Dead Zone: 50 mm fixed, set by where the float magnet sits on the end stop.
Total probe length = H1 + H2 + H3, rounded up to the nearest 50 mm. For a tank 1.2 m tall with full coverage, order a 1300 mm probe (50 + 1200 + 50).
Two real-world examples from quotes we shipped last quarter:
| Tank | Working Level Needed | Probe Ordered | Output Wired To |
|---|---|---|---|
| 2.5 m vertical day tank, diesel | 0 – 2.4 m | 2500 mm rigid, 4-20 mA HART | Allen-Bradley AI card |
| 0.8 m mixing vessel, IPA | 0.1 – 0.7 m | 800 mm rigid, Modbus RTU, Ex ia | Schneider M340 RS-485 |
| 4.2 m underground petrol tank | 0 – 4.0 m | 4200 mm rigid, 4-20 mA HART, Ex ia | Station controller |
Pricing and Lead Time
FOB Shanghai, EXW China for orders ≥ 5 units. Stock items ship in 5 working days; configured items 10-15 days.
| Configuration | Probe Length | Unit Price (USD, Qty 1-4) | Lead Time |
|---|---|---|---|
| SI-100 Standard, 4-20 mA | ≤ 1.0 m | $680 | 5 days (stock) |
| SI-100 Standard, 4-20 mA + HART | ≤ 2.0 m | $880 | 10 days |
| SI-100 Standard, Modbus RTU | ≤ 3.0 m | $1,150 | 10 days |
| SI-100 Ex ia, 4-20 mA + HART | ≤ 6.0 m | $1,650 | 15 days |
| SI-100 with Stilling-Well Chamber | Configured | $1,950 + | 15 days |
Bulk pricing (10+ units) drops 12-18 % depending on configuration. Quote turnaround is the same business day for any spec listed above.
If the SI-100 Doesn’t Fit Your Tank
Three alternatives we ship for the cases the rigid SI-100 cannot cover:
Flexible-Cable Magnetostrictive →
For tanks 6-23 m deep. Cable instead of rigid stem. Same accuracy, easier shipping.
Magnetic-Flap Level Gauge →
When you need a visible local indicator (flap column) plus the 4-20 mA signal in one device.
SMT3151 Hydrostatic →
Cheaper for water and benign liquids if ±0.1 mm is overkill. Submersible or threaded.
Frequently Asked Questions
What’s the Longest Rigid Probe You Will Build?
6 metres. Beyond that the rigid stem is hard to ship and to install, so we switch you to the flexible-cable variant which goes to 23 m.
Will It Work With Diesel That Has Water at the Bottom?
Yes, with two floats. The dual-float SI-100 gives you total liquid level (top float on diesel) and water-interface level (lower float on the diesel/water boundary). Specify on the quote.
Can I Retrofit It Where a Guided-Wave Radar Used to Be?
If the existing flange is DN50 or 1″ NPT, yes — drop-in. The 4-20 mA + HART output keeps your DCS configuration unchanged.
Does the Float Density Matter?
Standard SUS304 ring float works for liquids ≥ 0.6 g/cm³. For lighter liquids (like LPG condensate at 0.55 g/cm³) we ship a low-density titanium or PTFE float. Tell us the SG when you request the quote.
Which Output Should I Order for a Siemens S7-1500 PLC?
4-20 mA + HART for the simplest path (S7-1500 has analog input cards). If you are already on Profibus or Profinet, take the Modbus RTU version and run it through a gateway.
How Is the SI-100 Calibrated Before Shipping?
Each unit is bench-tested with the actual ordered float against a precision linear stage. A two-point calibration certificate (4 mA at empty, 20 mA at full) is included in the box. Field calibration is rarely needed.
Get a Confirmed Quote and PDF Datasheet
Tell us tank height, liquid, mounting style, and your PLC, and we will come back with a unit price and the full PDF datasheet within one business day.
Request a Quote
Wu Peng, born in 1980, is a highly respected and accomplished male engineer with extensive experience in the field of automation. With over 20 years of industry experience, Wu has made significant contributions to both academia and engineering projects.
Throughout his career, Wu Peng has participated in numerous national and international engineering projects. Some of his most notable projects include the development of an intelligent control system for oil refineries, the design of a cutting-edge distributed control system for petrochemical plants, and the optimization of control algorithms for natural gas pipelines.