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OTC Liquid Level Sensors


Low-Power, RS485 Modbus/ASCII Liquid Level Gauges

Float-based, Field-Proven Resistive Reed Switch Technology, US Patent 8,763,455 B1

RL3: Modbus | RL4: ASCII


  • Well suited for use in both hazardous and non-hazardous locations (oil & gas, petro-chemical, water and wastewater)
  • Applications requiring high scalability of up to 16 sensors from a single power source
  • Excellent choice for monitoring production levels and inventory management
  • Highly compatible with crude oil, diesel, kerosene, gasoline, variety of other hydrocarbons, and water


  • 3-in-1 continuous level measurement solution: product, interface & temperature
  • Safe for use in hazardous locations, Class I, Division 1 (Zone 0)
  • Intrinsically Safe when used with IS Safety Barrier Boards
  • Unaffected by electro-mechanical interference, tank turbulence or change in environmental conditions
  • Limited lifetime warranty against damage from H2S and paraffin buildup
  • Supports multiple fluid densities and wide temperature ranges
  • Requires only a one-time calibration, rarely requires cleaning, very low-maintenance product
  • Quick connect fitting eliminates sensor wiring error and hassle
  • Modbus RTU or LevelMaster ASCII Serial RS485 interface
  • Wireless option also available
  • Two material types: 316 Stainless Steel (up to 21 ft) or
    Flexible, PTFE (up to 38 ft)
  • 1/2” or 1/4” sensor resolution option
  • Click here to see level sensor accessories

Do More with Less

The OleumTech Resistive Level Sensor give you the ability to continuously measure product (oil), interface (water), and temperature from a single instrument, eliminating the need for multiple sensors and multiple tank ports.

No Wiring Hassle

Every Resistive Level Sensor is equipped with a quick connect fitting that joins the sensor to its head without any wires, eliminating wiring error and hassle to help you save valuable time during installation and troubleshooting.

Installs in Minutes

The flexible (PTFE) level sensor is only 20 inches in diameter when coiled  making extremely easy to transport. Deployment cost and time can be significantly reduced by enabling just one person to perform the entire installation.

High Scalability

Up to 16 of these low-power level sensing instruments can be multi-dropped using a single 12Vdc power supply. There are multiple 3/4-inch NPT ports available on the sensor head to help you run conduit and wire with ease.

Great Peace of Mind

The OleumTech Resistive Level Sensors are Intrinsically Safe and are certified for use in Class I, Division 1 (Zone 0) hazardous locations, providing the highest level of safety under rigorous, extreme outdoor conditions.

Maximum Flexibility

You can choose either Modbus RTU or LevelMaster ASCII communication protocol option for interfacing virtually any existing SCADA or control system. This digital level sensor is also available with wireless options.

Rigid - 316 Stainless Steel

Resistive Level Sensors are available with the rigid 316SS option, ranging from 2 to 21 ft in lengths with multiple float options. The rigid sensor comes equipped with a 3/4-inch NPT 1-inch NPT height adjustable compression fitting.

Flexible - PTFE

The liquid level probes can be ordered with the flexible (Polytetrafluoroethylene) option, ranging from 8 to 38 ft in lengths with multiple float options. This sensor provides a 1-inch NPT height adjustable compression fitting.

Choice is Yours

You can take advantage of the 1/4-inch resolution version of the sensor with ±1/8-inch accuracy or take a more cost-effective approach by using the 1/2-inch resolution version that provides ±1/4-inch accuracy.

Ultimate Level Sensing Solution

The OleumTech® H-Series Resistive Tank Level Sensors are one of the best selling and top of the class level monitoring solutions available for use in hazardous and ordinary locations. This liquid level instrument is designed to measure three separate or distinct processes: product, interface, and temperature levels.

OleumTech’s patented Automatic Tank Gauges (ATGs) are offered in both flexible (PTFE) and rigid (316 SS) materials in various custom lengths. The 1/4” resolution sensors mate with the HW5800-RL3 and HW5800-RL4 sensor heads while the 1/2” resolution sensors mate with the HW5000-RL3 and HW5000-RL4 sensor heads.

Reliable, Scalable, and Safe

The field-proven level sensor can communicate with any Modbus RTU master or LevelMaster device via RS485 Serial connection. The low-power Resistive Level Sensor can be multi-dropped of up to 16 sensors. Additional data such as volume and tank full percentage can be calculated and reported as well, along with the core level variables. The Resistive Level Sensor is certified for use in Class I, Division 1 (Zone 0) hazardous locations.

This product is also available with wireless connectivity and a local display.

This product is also available with wireless connectivity.


The Resistive Level Sensors are ideal for use as oil level sensors, water level sensors for storage tanks that contain either or both liquid densities. These level instruments are widely used in oil production tank batteries, condensate tanks, water treatment centers, petrochemical and chemical-making plants, wastewater handling and storage facilities, refineries, and power generating plants.

Safety∙ Intrinsically Safe for Use in Hazardous Environments
∙ Class I, Division 1, Groups C, D T4; Ex ia IIB T4 Ga; Class I, Zone 0, AEx ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
∙ ATEX: Sira 16ATEX2229X; Ex ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
∙ IECEx: SIR 16.0079X; Ex ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
Device Functionality∙ Serial Resistive Level Sensor
RL3/RL3-T: Modbus, 3-in-1 Measurement Capability: Product, Interface and Temperature
RL4/RL4-T: LevelMaster ASCII, 3-in-1 Measurement Capability: Product, Interface and Temperature
Embedded Controller∙ Ultra-Low Power RISC Microcontroller with Internal FLASH (Field Upgradeable)
Configuration∙ USB to RS485 Converter (SX1000-CC8)
Sensor Type∙ Resistive
Resolution∙ High Resolution, Depends on Sensor: 1/4" (6.4 mm) or 1/2" (12.7 mm)
Accuracy∙ ±1/8-inch for 1/4-inch Resolution Sensor ; ±1/4-inch for 1/2-inch Resolution Sensor
∙ ±3.2 mm for 6.4 mm Resolution Sensor ; ±6.4 mm for 12.7 mm Resolution Sensor
Power Source∙ External 6-12 Vdc (12 Vdc Max)
Self-Diagnostics∙ Contains Comprehensive Self-Checking Software and Hardware for Continuous Monitoring of Operation
Communication∙ Modbus or LevelMaster ASCII
Baud Rate∙ 1200-115200 bps
Dimensions∙ 5" (W) x 7.6" (H) x 4.4" (D) / 127 mm (W) x 193 mm (H) x 112 mm (D)
Package Dimensions ∙ 10.25" (W) x 14" (H) x 6.5" (D) / 260 mm (W) x 356 mm (H) x 165 mm (D)
Package Weight∙ ~4.5 lbs/ 2.0 kg
Connection Fitting∙ 3/4" NPT Female
Enclosure Casing Material∙ Type 4X Aluminum; IP66
DC Power Input∙ 6-12 Vdc (12 V Max)
Power Consumption∙ 5.4 mA Max @ 6-12 Vdc
IS Safety Protection∙ Barrier Board (SX1000-BB1)
RIGID: 316 Stainless Steel "SS"
FLEX: Polytetrafluoroethylene "PTFE"
Extremely Reliable and Accurate Resistive Reed Switch Technology
Measurement Capabilities (3-in-1)
Product, Interface, and Temperature
Lengths Offered in US Units
2 to 21 ft Length in 1 ft Increments
8 to 38 ft Length in 1 ft Increments
Lengths Offered in Metric
0.61 to 6.4 m in 0.31 m increments
2.44 to 11.58 m in 0.31 m increments
Resolution and Accuracy
Option 1: 1/2-inch (12.7 mm) Resolution with ±1/4-inch ( ±6.4 mm) Accuracy (6-pin Quick Connect)
Option 2: 1/4-inch (6.4 mm) Resolution with ±1/8-inch (±3.2 mm) Accuracy (8-pin Quick Connect)
Sensor to Interface Mating Connection (No Wiring Solution)
316 SS Quick Connect: 6-pin Connection for 1/2" Resolution, 8-pin Connection for 1/4" Resolution
Tank Mating Connection (Adjustable Compression Fitting)
3/4" NPT Male
1" NPT Male
Temperature Accuracy
±1 °C
Sensor Rod/Tubing Diameter
0.68" (17 mm): 15 ft Sensor or Shorter
0.85" (22 mm)
0.85" (22 mm): 16 ft Sensor or Taller
Anchor Weight Diameter
2.4" / 60.3 mm
Height of Anchor Weight
8 to 19 ft sensor: 5"
20 - 28 ft sensor: 6.75" / 29 - 38 ft sensor: 8"
Coiled Diameter
20" (50.8 cm) Coiled Diameter
Minimum Measurement from Bottom (Deadband)
2" (50.8 mm) from Bottom
From Top of Anchor Weight
Pressure Rating
Float Dependent
Float Dependent
Sensor Only without Float(s)
569 PSI / 39 Bar
142 PSI / 9.8 Bar
Sensor w/ 316 SS Float - Standard*
440 PSI / 30 Bar
Sensor w/ 316 SS Float - Large
363 PSI / 25 Bar
142 PSI / 9.8 Bar
Sensor w/ Polypropylene (PP) Float
72 PSI / 5 Bar
72 PSI / 5 Bar
Float Options:
*316 Stainless Steel - Standard, 440 PSI/30 Bar
Compatible Only with Rigid Sensor Length up to 15 ft Prod: 0.64 SG, Intf: 0.96 SG, ID 0.72" (18.3 mm)
OD 2.05" (52.1 mm), Inner Clearance: 0.1" (2.6 mm)
316 Stainless Steel - Large, 363 PSI/25 Bar
Product: 0.62 SG, Interface: 0.95 SG, ID 1.1" (27.9 mm), OD 2.76" (70.1 mm), Inner Clearance: 0.5" (12.7 mm)
Polypropylene (PP), 72 PSI/5 Bar
Product: 0.64 SG, Interface: 0.96 SG, ID 1.1" (27.9 mm), OD 2.91" (73.9 mm), Inner Clearance: 0.5" (12.7 mm)
Operating Temp. Sensing Area
-40 °F to 248 °F (-40 °C to 120 °C)
Class I, Division 1, Groups C, D T4; Ex ia IIB T4 Ga; Class I, Zone 0, AEx ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
ATEX: Sira 16ATEX2229X; Ex ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
IECEx: SIR 16.0079X; Ex ia IIB T4 Ga, -40 °C ≤ Tamb ≤ 70 °C
Power (Wireless)
SX1000-BP3, 3.6 V Lithium Replaceable Battery Pack, 10-Year Life @ 1 min Read Interval
Power (Hardwired)
External 6-12 Vdc (12 V max), 5.4 mA @ 6-12 Vdc
Wireless Compatibility
OTC - WT / SM Series Resistive Transmitters and Sigfox-enabled Resistive Transmitters
Hardwire Serial Interface (H-Series Only)
RS485, 2-Wire, 16 or 32-bit Modbus RTU, LevelMaster ASCII, Termination for Daisy-chain
Minimum Sensor Read Interval
Down to 5 Seconds
Model #: 1/2" Resolution with ±1/4-inch Accuracy
Model #:1/4" Resolution with ±1/8-inch Accuracy
Kit #: 1/2" Resolution with Float(s)
Kit #: 1/4" Resolution with Float(s)
Operating Conditions∙ Ambient Temperature (Class I, Division 1): -40 °F to 158 °F (-40 °C to 70 °C)
∙ Ambient Temperature (Non-Hazardous Applications): -40 °F to 176 °F (-40 °C to 80 °C)
∙ Humidity: 0 to 99 %, Non-Condensing
Warranty∙ 2-Year Parts and Labor
Country of Origin∙ USA
Model Numbers∙ 1/2" Resolution (6-pin): HW5000-RL3 (Modbus), HW5000-RL4 (LevelMaster ASCII)
∙ 1/4" Resolution (8-pin): HW5000-RL3-T (Modbus), HW5000-RL4-T (LevelMaster ASCII)
Barrier Boards∙ SX1000-BB1
Configuration Kit∙ H-Series Configuration Kit (SX1000-CC8)


Wireless Level Sensors

Best-in-class tank level gauge and wireless interface combination for self-contained, battery-powered standalone operation.

Hydrostatic Level Sensors

Cost-effective wireless level monitoring solution using a low-power 1-5 V analog submersible hydrostatic pressure transducer.

Ulrasonic Level Sensors

Low-maintenance, low-power, non-contact, non-moving level measurement solution designed specifically for monitoring water.

High Level Switches

Instantly detect high level conditions for providing overfill  protection and  spills prevention. Detect high and high-high levels.