Flexar Guided Wave Radar Level Sensor TDR




Proven Flexar® Technology Installed In Thousands Of Bulk Solids Applications
Reliable TDR (a.k.a Reflex Radar) Technology Used For Decades
“Smart” Transmitter Output For Use With Industry-Leading SiloTrack™ Inventory Management Software
Measuring Range Up To 100ft (30m) In Solids And 200ft (60m) In Liquids
Unaffected By Airborne Dust, Bulk Density, Temperature, And Other Properties – Ideal For Powders And Pneumatically Filled Solid
Process Temperatures To +300°F (150°C)
No Field Calibration Required - Easy To Install And Setup
Optional Analog Output For Easy Connection To Existing Control Systems Or Indicating Devices
Wireless Sensor Interface Solutions (Click Here)
SiloTrack(TM) PC-Based Inventory Management Solutions (Click Here)
HMI2 Local Operator Interface Option (Click Here)

Contact MonitorNeed some more information?...Click on the button.


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Product Overview



Principle of Operation

Probe Styles



Inventory Mgt Software

HMI2 Control Console



Similar Item(s):

RadarRight - Radar Level Sensor - Non Contact Silo Patrol Smart Plumb Bob Level Sensor
RadarRight(TM) Non-Contact Continuous Level Sensor SiloPatrol® Continuous Level Sensor



The Flexar® continuous level measurement system is a smart guided wave radar device used for monitoring the level of powders, granules and other bulk solids as well as many liquids and slurries. It is also suitable for use with a variety of liquids and some slurries. It is used in a wide assortment of vessels and industries for measuring levels up to 200ft (60m) in height. Bringing the Pieces Together: Manufactured at our facility in Elburn, IL, we uniquely combine this proven and strategically acquired technology with almost five decades of expertise and focus in powder and bulk solids applications, and with our SiloTrack™ inventory management software interface. Monitor Technologies uniquely provides the best solutions in level measurement and inventory management of powders and bulk solids. The Flexar guided wave radar level sensor and/or transmitter requires no field calibration or re-calibration and can be setup easily by customer personnel without the use of any special tools or training. Flexar units are suited for almost any application, can operate with process temperatures up to 392° F (200°C), can be provided with a variety of process connections and can work reliably with materials having a wide range of bulk densities and dielectric constants. Flexar is available with a choice of two outputs. The standard output is a “smart” interface for use with SiloTrack™ Version 3.5 PC-based inventory management software. This network-ready software provides a flexible graphical interface for up to 128 “smart” output sensors. In lieu of this “smart” output, an optional analog output is also available.

Principle of Operation

Flexar® smart guided wave radar level sensors and transmitters operate using TDR (time domain reflectometry) principles that were first developed in the middle part of the 20th century for use in the geological field. Further development of TDR led to its use in the telecommunication industry for detecting breaks in cables. Flexar technology was pioneered in the mid-late 1990’s when TDR was applied to level measuring applications within the process measurement industry.

In the application of TDR for process level measurement micro-pulses are continuously transmitted along a probe or “wave guide” at the speed of light. As soon as the pulses reach the material surface they reflect back to the sensor electronics unit. The time-of-flight of the pulses is calculated and directly related to the distance from the point at which the sensor is mounted on the top of the vessel to the material surface (level). The output from the electronics is continuously updated as the level of the material surface changes.

Flexar smart guided wave radar sensors are equipped with two different measuring modes. In the Direct measuring mode the pulses directly reflect off the material surface back to the electronics unit. This mode is used in applications where the material being measured has a dielectric constant as low as 2.1 for single-cable/rod probes and 1.8 for twin-cable probes.

For materials with dielectric constant below the above mentioned limits, down to as low as 1.4, the second measurement mode is used. This is the TBF (tank bottom following) mode, which is used due to the inability of the pulses to adequately reflect off of the surface of very low dielectric materials. In this measuring mode the Flexar sensor has a “short circuit” at the bottom of the probe at a precisely known distance from the sensor’s mounting point.

In the TBF mode the pulses travel through air at the speed of light and then pass through the material in the vessel at a slower speed, dependent on the specific dielectric constant. The pulses are reflected at the short circuit back up the probe. Flexar sensors in the TBF mode measure the time between the emission and reception of the pulses from the probe short circuit. Because the return time of a pulse when no material is present (through air) is known, we can determine the difference in time between the time-of-flight when empty and the time-of-flight when filled as being directly proportional to the material level in the vessel.




The Flexar® smart guided wave radar continuous level measuring system can be used in a wide variety of applications, including powders, coarse/fine granular solids, liquids, foodstuffs and even some corrosive substances. Flexar sensor technology is proven in many difficult applications including those where dust levels make it difficult for other technologies to perform reliably, especially at long ranges.

Please consult Monitor's Technical Support Dept. to verify that the Flexar is the best fit for your specific application. Certain conditions (like target material dielectric, silo height, etc.) need to be taken into consideration.

Typical Applications include, but are not limited to:



Bulk Chemicals




Carbon Black

Coal Dust

Some Liquids

Fly Ash




PVC Powder





Flexar Silo Level Installation
The maximum range for solids applications is limited to 100ft (30m) due to load limits possible from heavy materials in long ranges. Liquid applications can extend up to 200ft (60m). Any application requiring a continuous level measurement update where the process temperature does not exceed 392° F (200°C) and 580psig (40bar) is possible. The 316 stainless steel probes and threaded or flanged process connections make the Flexar continuous level measuring system ideal for almost any bulk solid and liquid application. To ensure a successful and reliable application, consult with the Monitor Technologies factory-based technical support group to see if Flexar is right for your application.





If material levels need to be monitored at one or many locations (i.e. your facility, a location down the street, or a plant on the other side of the world) the Flexar® system can provide accurate and reliable measurements. Using SiloTrack™ Version 3.5 software, inventory monitoring from remote locations has never been easier.

Silo Track Level Inventory Management Software









Using the available WirelessEZ interface in your application may help you reduce the installed cost of your SiloTrack™ / Flexar® system even further. The WirelessEZ transceivers use frequency-hopping spread-spectrum wireless technology and operate in the FCC license-free 900MHz band. This provides the longest range and most reliable wireless communications available. Working in conjunction with SiloTrack™ PC-Based inventory management software, the WirelessEZ transceivers provide the most functional and economical inventory management system available today.

Click here for more details on the WirelessEZ and contact our technical support personnel today to see if your application can benefit from a wireless communications solution.

Wireless EZ Level Control



A unique feature of the Flexar® Inventory Management System is the ability to incorporate both relay and analog outputs with a standard "smart" output sensor system. These auxiliary relay and/or analog outputs are provided in Auxiliary Output Enclosures (AOE) and are programmed and controlled by either the HMI2 or SiloTrack™ PC-based Inventory Management Software. One analog output and up to four relays (two for HMI2; four for SiloTrack) can be assigned to each of the “smart” output sensors. These can be used to tie the Inventory Management System into remote control systems, sound alarms and for local control functions. Up to 16 analog outputs or 32 relays can be provided within a single enclosure. Up to four AOE’s can be connected on a single network. The AOE can be located close to the point of hardwiring termination minimizing wiring and installation costs.


2-Card AOE


Solid-State Performance, No Moving Parts...
Unlike weight and cable based systems of old, Flexar® guided wave radar level sensors are state-of-the-art and use a time-proven electronic method for continuous measurement of a material level. This non-mechanical means of measurement helps ensure low maintenance.

Measure Materials With Dielectric > 1.4 (TBF Mode)...
Flexar sensors are capable of sensing and measuring the level of most any material. Materials with dielectric constants below 1.8-2.1 require the use of our TBF (tank bottom following) measuring mode.

Unaffected By Dust And Changes In Material Properties...
The technology employed in Flexar units has been proven to be unaffected by airborne dust even during pneumatic filling operations. Unlike through-air technologies such as ultrasonic, through-air radar and laser, Flexar can reliably measure in dusty environments without sacrificing performance or reliability.

Range Of Probes...
In order to handle the assortment of applications possible with Flexar, Monitor offers a range of probe styles including single-cable, twin-cable and single-rod. All probes are constructed of 316 stainless steel, have traction load handling capabilities suitable for their respective applications and are easily field replaceable. Consult with Monitor’s factory-based technical support personnel to select the right probe style for your application.

Assortment Of Process Connections...
To meet the required bulk solids and liquid applications we have prepared a selection of process connections that will ensure a smooth and simple installation. Flexar sensors can be provided with 1-1/2” NPT, 1-1/2” BSP G, 2” ANSI or DIN DN50PN40 flange connections. Probe type will determine the available process connections.

Dual Compartment Enclosure...
The Flexar smart guided wave radar sensor uses an enclosure with two compartments, each with its own access cover. This allows separation of access for wiring and setup/display. The setup/display compartment is provided with a cover window allowing local viewing of the LCD display. In addition, every unit is provided with either two 1/2” NPT conduit entrances (NPT threaded and ANSI flanged process connections) or M20 cable connectors (BSP threaded and DN flanged process connections).

Local LCD Display And Setup...
Each sensor includes a built-in user interface consisting of a three-line backlit LCD display, three pushbuttons and three magnetic sensors (used to perform setup and interact with the unit without having to remove the display cover).

Universal Power Supply...
Power supply choices include a universal high voltage option 100-240 VAC and a low voltage 24 VAC/VDC option.

Choice of outputs...
The standard output for all Flexar guided wave radar units is a “smart” RS-485 communications interface for use with SiloTrack™ Version 3.5 inventory management software. In lieu of this “smart” interface an analog 4-20mA output is available.

Remote electronics available...
The standard unit includes the electronics integrally mounted with the sensor. However, remote mounted electronics is optionally available for applications where the electronics are desired to be mounted away from the probe due to extreme vibration, temperature or for convenient access to the local operator interface. The remote electronics version includes a pre-wired 16.4ft (5m) interconnecting cable.

All units include the CE mark and are approved for use in ordinary locations.



Probe Styles

Single Cable 0.16” (4mm)

Single Cable 0.31” (8mm)

Single flexible 316 SS cable with counterweight

Single Flexible 316 SS cable with large or small counterweight

Vessel height < 150ft (45m); Liquids; Some solids
(consult Monitor)

Vessel height < 100ft (30m);
Powders and other bulk solids (consult Monitor)


Twin Cable 0.16” (4mm)

Single Rod 0.38” (10mm)

Two flexible 316 SS cables with spacers between them at intervals, w/ counterweight

Single 316 SS rigid rod

Vessel height < 200ft (60m); Low dielectric liquids, some granules (consult Monitor)

Vessel height < 10ft (3m); Liquids; Some powders (consult Monitor)

HMI2 Operator Interface Control Console

HMI2 Operator Interface

The HMI2 operator interface control console provides convenient, local interface for Monitor’s “Smart” RS-485 SiloPatrol® SMU SE cable-based inventory monitoring sensors and/or Flexar® guided wave radar sensors. HMI2 allows for monitoring up to 32 SMU and/or Flexar sensors. The multi-functional HMI2 controls sensor operations, displays measured and calculated data and performs/displays system and sensor diagnostic messages. The HMI2 is easily programmed to display calculated level, volume, weight or percent in addition to the basic distance measurement. Manual readings are taken by depressing the MEAS button, followed by the channel number, followed by ENTER. The HMI2 can also be programmed to operate the SMU “Smart” RS-485 sensors automatically. Menu options allow the user to select days of SMU operation (such as Mon.-Fri.), time window (such as 7 a.m.-3 p.m.) and measurement interval (minimum 30 minutes).

Click Here for more details on the HMI2


SiloTrack(TM) PC-Based Inventory Management Software
Silo Track Inventory Software
SiloTrack™ Version 3.5 Inventory Management Software provides users with an unsurpassed, flexible graphical interface for SiloPatrol® SE “smart” output sensors. Together, SiloTrack Server and Client software can provide inventory monitoring and management to a virtually unlimited number of users, both internal and external to your facility. This allows easy implementation of remote monitoring and vendor managed inventory programs.

SiloTrack capabilities include:
- Monitor up to 128 sensors/with up to 5 sensors per vessel
- Easy to set up and use
- Network capable
- Remote monitoring via LAN, Internet/WAN or dial-up
- Available in English/Spanish language
- Automatic and manual measurement initiation
- Curve-fit weight table
- Enhanced 3-D type silo graphics
- Export silo history and alarm data
- Automatic Reports and Scheduling
- Set up four alarms per silo
- Alarm notification via e-mail, fax, etc.

Click Here for more details on SiloTrack



Power Requirements:

100-240VAC (+10%/- 15%); 9VA; 50/60Hz or
24VAC/VDC (+10%/- 15%); 9VA/W


6562ft (2000m) maximum

Installation Category:


Pollution Degree:

4 (reduced to 2 by enclosure) Suitable for indoor/outdoor use

Process Temperature:

Ordinary Location Units

-20°F to +300°F (-30°C to +150°C);



Ambient Temperature:

-5°F to +120°F (-20°C to +50°C)

Operating Pressure:

1-1/2” NPT

-14.5psig to +580psig (-1bar to +40bar)

G 1-1/2 (1-1/2” BSP):

-14.5psig to +580psig (-1bar to +40bar)

2” ANSI:

-14.5 psig to 150 psig (-1bar to 10bar)


-14.5psig to +580psig (-1bar to +40bar)

Measurement Range:

Single Cable 0.16” (4mm):

150ft (45m)

Single Cable 0.31” (8mm):

100ft (30m)

Twin Cable 0.16” (4mm):

200ft (60m)

Single Rod .38” (10mm):

10ft (3m)



Direct Mode: Solids

± 0.8” (20mm)


< 20ft (6m): ± 0.2” (5mm)
≥ 20ft (6m): ± 0.2” (5mm) + 0.02% of distance measured

TBF Mode (All):

± 0.8” (20mm) when Dielectric is constant


± 0.04” (1mm)


± 0.012” (0.3mm)

Minimum Dielectric Constant:

Direct Mode

Twin Cable ≥ 1.8; Single Cable/Rod ≥ 2.1

TBF Mode

All Probe Styles ≥ 1.4

Process Mounting Connection:

Single Cable/Rod Only

1-1/2” NPT; G 1-1/2 (1-1/2” BSP)

All probe Styles

2” ANSI 150lb. Flange; DN50PN40 Flange

Conduit/Cable Entry:

NPT/ANSI Process Connections

(2) 1/2” NPT

BSP/DN Process Connections

(2) M20 x 1.5 cable connectors

Probe Styles:


Single Cable:0.16” (4mm)


Single Cable:0.31” (8mm)


Single Rod

316SS; 0.38” (10mm) diameter;

Twin Cable

316SS; Two 0.16” (4mm) cables; FEP spacers




18lb (8kg) without probe for ordinary location;
20lb (9kg) without probe for hazardous location;

Single Cable
0.16” (4mm)

0.08lb/ft (0.12kg/m)

Single Cable 0.31” (8mm)

0.28lb/ft (0.41kg/m)

Single Rod

0.42lb/ft (0.62kg/m)

Twin Cable

double weight of 4mm cables above for twin cable

Maximum Traction Loading:

0.31” (8mm) Single Cable

7,700lbs/3.9 tons (3.5 metric tons)

0.16” (4mm) Single Cable

2250lbs/1.1 tons (1.02 metric tons)

Minimum Separation From Objects:

Single Cable/Rod

12” (300mm)

Twin Cable

4” (100mm)

Output Signal:



RS-485, half-duplex, isolated, proprietary protocol


4-20mA; 350ohms maximum load

Wiring Distance (“smart” output):

4,000ft (1,220m)

Local Display:

3-line; Backlit LCD; 3 pushbuttons;
3 magnetic sensors for setup without cover removal

Materials of Construction:


Aluminumm, powder coated

Threaded/Flange Connection:

316 Stainless Steel

Process Insulator:

Teflon (PTFE)

O-Ring Seal:



316 Stainless Steel

Remote Electronics:

16.4’ (5m) pre-wired interconnection cable

Dead Zones:


Single Cable/Rod


Dielectric = 80 (water)

Top = 15.75” (400mm)
Bottom = 0.8” (20mm)

Dielectric = 2.4 (oil)

Top = 19.7” (500mm)
Bottom = 3.9” (100mm)

Twin Cable


Dielectric = 80 (water)

Top = 9.8” (250mm)
Bottom = 0.8” (20mm)

Dielectric = 2.4 (oil)

Top = 13.0” (330mm)
Bottom = 0.8” (20mm)

Enclosure Rating:




Integral Electronics Only

Ordinary Location

CE Mark


Remote Electronics

Ordinary Location

CE Mark

Hazardous Location



Teflon® is a registered trademark of Dupont Chemical Co.
Windows® is a registered trademarks of the Microsoft Corporation
RSView® is a registered trademark of Rockwell Automation
Wonderware® is a registered trademark of Wonderware Corporation
Intellution® is a registered trademark of Intellution, Inc.
Cimplicity® is a registered trademark of General Electric Company
Bluetooth® is a registered trademark of Bluetooth SIG, Inc.
AndroidTM is a trademark of Google Inc.
ModbusTM is a trademark of Schneider Electric / Modicon



Monitor Technologies LLC warrants each Flexar® guided wave radar continuous level measurement system and HMI2 it manufactures to be free from defects in material and workmanship under normal use and service within two (2) years from the date of purchase. The purchaser must give notice of any defect to Monitor within the warranty period, return the product intact and pre-paid transportation charges. The obligation of Monitor Technologies LLC under warranty is limited to repair or replacement at its factory. This warranty shall not apply to any product which is repaired or altered outside of the Monitor Technologies LLC factory, or which has been subject to misuse, negligence, accident, incorrect wiring by others or improper installation. Monitor Technologies LLC reserves the right to change the design and/or specifications without prior notice.

Part Numbers / Product Configurations

Part # > Product Configuration

16-8111-1111 > FLEXAR,485,S-CBL,O/L,VHI,1-1/2 NPT
16-8111-1131 > FLEXAR,485,S-CBL,O/L,VHI,2"ANSI
16-8111-1141 > FLEXAR,485,S-CBL,O/L,VHI,DN50PN40
16-8111-1211 > FLEXAR,485,S-CBL,O/L,VLO,1-1/2 NPT
16-8111-1231 > FLEXAR,485,S-CBL,O/L,VLO,2"ANSI
16-8111-1241 > FLEXAR,485,S-CBL,O/L,VLO,DN50PN40
16-8112-1112 > FLEXAR,485,LL-CBL,O/L,VHI,1-1/2 NPT
16-8112-1113 > FLEXAR,485,LS-CBL,O/L,VHI,1-1/2 NPT
16-8112-1132 > FLEXAR,485,LL-CBL,O/L,VHI,2"ANSI
16-8112-1133 > FLEXAR,485,LS-CBL,O/L,VHI,2"ANSI
16-8112-1142 > FLEXAR,485,LL-CBL,O/L,VHI,DN50PN40
16-8112-1143 > FLEXAR,485,LS-CBL,O/L,VHI,DN50PN40
16-8112-1212 > FLEXAR,485,LL-CBL,O/L,VLO,1-1/2 NPT
16-8112-1213 > FLEXAR,485,LS-CBL,O/L,VLO,1-1/2 NPT
16-8112-1232 > FLEXAR,485,LL-CBL,O/L,VLO,2"ANSI
16-8112-1233 > FLEXAR,485,LS-CBL,O/L,VLO,2"ANSI
16-8112-1242 > FLEXAR,485,LL-CBL,O/L,VLO,DN50PN40
16-8112-1243 > FLEXAR,485,LS-CBL,O/L,VLO,DN50PN40
16-8113-1134 > FLEXAR,485,2-CBL,O/L,VHI,2"ANSI
16-8113-1144 > FLEXAR,485,2-CBL,O/L,VHI,DN50PN40
16-8113-1234 > FLEXAR,485,2-CBL,O/L,VLO,2"ANSI
16-8113-1244 > FLEXAR,485,2-CBL,O/L,VLO,DN50PN40
16-8114-1115 > FLEXAR,485,1-ROD,O/L,VHI,1-1/2 NPT
16-8114-1135 > FLEXAR,485,1-ROD,O/L,VHI,2"ANSI
16-8114-1145 > FLEXAR,485,1-ROD,O/L,VHI,DN50PN40
16-8114-1215 > FLEXAR,485,1-ROD,O/L,VLO,1-1/2 NPT
16-8114-1235 > FLEXAR,485,1-ROD,O/L,VLO,2"ANSI
16-8114-1245 > FLEXAR,485,1-ROD,O/L,VLO,DN50PN40
16-8121-1111 > FLEXAR,4-20,S-CBL,O/L,VHI,1-1/2 NPT
16-8121-1121 > FLEXAR,4-20,S-CBL,O/L,VHI,1-1/2 G
16-8121-1131 > FLEXAR,4-20,S-CBL,O/L,VHI,2"ANSI
16-8121-1141 > FLEXAR,4-20,S-CBL,O/L,VHI,DN50PN40
16-8121-1211 > FLEXAR,4-20,S-CBL,O/L,VLO,1-1/2 NPT
16-8121-1231 > FLEXAR,4-20,S-CBL,O/L,VLO,2"ANSI
16-8121-1241 > FLEXAR,4-20,S-CBL,O/L,VLO,DN50PN40
16-8122-1112 > FLEXAR,4-20,LL-CBL,O/L,VHI,1-1/2 NT
16-8122-1113 > FLEXAR,4-20,LS-CBL,O/L,VHI,1-1/2 NT
16-8122-1122 > FLEXAR,4-20,LL-CBL,O/L,VHI,1-1/2 G
16-8122-1123 > FLEXAR,4-20,LS-CBL,O/L,VHI,1-1/2 G
16-8122-1132 > FLEXAR,4-20,LL-CBL,O/L,VHI,2"ANSI
16-8122-1133 > FLEXAR,4-20,LS-CBL,O/L,VHI,2"ANSI
16-8122-1142 > FLEXAR,4-20,LL-CBL,O/L,VHI,DN50PN40
16-8122-1143 > FLEXAR,4-20,LS-CBL,O/L,VHI,DN50PN40
16-8122-1212 > FLEXAR,4-20,LL-CBL,O/L,VLO,1-1/2 NT
16-8122-1213 > FLEXAR,4-20,LS-CBL,O/L,VLO,1-1/2 NT
16-8122-1222 > FLEXAR,4-20,LL-CBL,O/L,VLO,1-1/2 G
16-8122-1232 > FLEXAR,4-20,LL-CBL,O/L,VLO,2"ANSI
16-8122-1233 > FLEXAR,4-20,LS-CBL,O/L,VLO,2"ANSI
16-8122-1242 > FLEXAR,4-20,LL-CBL,O/L,VLO,DN50PN40
16-8122-1243 > FLEXAR,4-20,LS-CBL,O/L,VLO,DN50PN40
16-8123-1134 > FLEXAR,4-20,2-CBL,O/L,VHI,2"ANSI
16-8123-1144 > FLEXAR,4-20,2-CBL,O/L,VHI,DN50PN40
16-8123-1234 > FLEXAR,4-20,2-CBL,O/L,VLO,2"ANSI
16-8123-1244 > FLEXAR,4-20,2-CBL,O/L,VLO,DN50PN40
16-8124-1115 > FLEXAR,4-20,1-ROD,O/L,VHI,1-1/2 NPT
16-8124-1135 > FLEXAR,4-20,1-ROD,O/L,VHI,2"ANSI
16-8124-1145 > FLEXAR,4-20,1-ROD,O/L,VHI,DN50PN40
16-8124-1215 > FLEXAR,4-20,1-ROD,O/L,VLO,1-1/2 NPT
16-8124-1235 > FLEXAR,4-20,1-ROD,O/L,VLO,2"ANSI
16-8124-1245 > FLEXAR,4-20,1-ROD,O/L,VLO,DN50PN40
16-8131-1111 > FLEXAR,485/4-20,S-CBL,O/L,VHI,1-1/2
16-8132-1112 > FLEXAR,485/4-20,LL-CBL,O/L,VHI,NPT
16-8132-1113 > FLEXAR,485/4-20,LS-CBL,O/L,VHI,NPT
16-8132-1132 > FLEXAR,485/4-20,LL-CBL,O/L,VHI,2"AN
16-8132-1212 > FLEXAR,485/4-20,LL-CBL,O/L,VLO,NPT
16-8221-1111 > FLEXAR,RMT,4-20,S-CBL,O/L,VH1,1-1/2
16-8222-1112 > FLEXAR,RMT,4-20,LL-CBL,O/L,1-1/2 NT
16-8222-1212 > FLEXAR,RMT,4-20,LL-CBL,O/L,1-1/2 NT
16-8231-1211 > FLEXAR,RMT,485/4-20,S-CBL,O/L,VLO,1


Last Rev.: January 01, 2019