Density Measurement with Uni-Probe LB 491

The measuring system Uni-Probe LB 491 is used for the non-contacting measurement of density and concentration on liquids, slurries or bulk materials. Connected to a velocity measurement, the Uni-Probe LB 491 can also be used for the online determination of mass flow.

The Uni-Probe LB 491 is a compact field device, combining both detector and evaluation in one single instrument. It provides interfaces for

  • HART
  • Profibus PA
  • Foundation Fieldbus

In addition the separate 4-20mA current output can always be used as alternative signal output.



CrystalSENS Detector

Point detector with high-sensitive, high-quality Sodium Iodide crystal for best long-term stability.

SuperSENS Detector

Best sensitivity on the market, is able to work with smallest source activities.
LB 491
Detector operating data 
Power supply100 ... 240 VAC, ±10%, 50 ... 60 Hz, 15 VA
24 VDC (18 ... 32 VDC), 15 W; 24 VAC + 10%/-15%,
50 ... 60 Hz, 15 VA

Cable connections

4 cable entries 3/4“ inch, NPT, sealed with dummy plugs Option: metric adapters and cable glands on request

Maximum cable length

3300 m (120 L)), 1600 m (250 L)), 800 m (500 L))

Wire cross section

0,5 ... 1,5 mm2

Housing materialStainless steel ISO 1.4301 / AISI 304
Water coolingOption, max. 6 bar
Scintillator Size Ø x lenght [mm]
(point detectors)
50 x 50 NaI (Tl)
SuperSENS150 x 150 polymer
Ambient temperature
(Operation and storage)
-40 ... +60°C (-40 ... +140°F) for NaI (Tl) and / or
-40 ... + 55°C (-40 ... +131°F) for polymer
Observe possible temp. restrictions for Ex-protection!
for 100...240 VAC version, operation only up to max. 50°C
Temperature stability≤0.002%/°C (-40 ... +50°C) for NaI (Tl) and/ or
≤0.01%/°C (-40 ... +50°C) for polymer
Detector certificates & tests 


IP65 / IP66 + Nema 4X

Explosion protection

II 2 GD EEx d IIB T5 IP66 T80°C                      -40 ... +80°C
II 2 GD EEx d IIC T6 IP66 T80°C                      -40 ... +60°C
(...+50°C for LB 490 TowerSENS and SuperSENS)
II 2 GD EEx d [ia] IIC T6 IP66 T80°C                -20 ... +50°C

Class I Division 1 Group A,B,C,D
Class II Division 1 Group E,F,G                        -40 ... +50°C

Other certificatesNepsi, IECEx, Kosha, CCOE, others upon request
Signal inputs and outputs 

Signal output

HART 4 ... 20 mA floating, active or passive, to Namur NE 43 max. impedance: 500 L) (when active)

Power supply: 12 V ... 24 V (passive)

max. impedance at 12 V: 250 L) or 24 V: 500 L) (passive)

Option: intrinsically safe HART current output 4...20 mA
Exi IIB: Lo=14.78 mH; Co=679 nF /
Exi IIC: Lo=2.18 mH; Co=84 nF

Bus output - option

Bus interface: Profibus PA or Foundation Fieldbus
Bus powered, typically 13 mA with 2xAI function blocks Option:
intrinsically safe bus interface, 20 m signal cable (blue)

Option: intrinsically safe Bus interface
Approval according to ATEX and FISCO

Digital inputsDig In 1: Hold input, Dig In 2: Empty adjustment
Analogue inputPt100 for temperature compensation

0/4 ... 20 mA for speed signal at mass flow measurement in the pipeline

Digital outputs1 relay (SPDT) for collective fault message
3 relays (SPDT) alternatively for: Hold signal, min./max. alarm, Detector temperature, radiation interference detection

Permissible load at ohmic load: max. 5 A at 250 VAC or 30 VDC


RS 232 for software update

Data backup

in non-volatile memory

User interface

HART Communicator

Delta V AMS

Simatic PDM



Format Size
Densidad y Concentracion solidos Spanish language en PDF 2.65 MB
Density measurement - system overview en PDF 1.57 MB
Medicao de Densidade e Concentracao Portuguese language en PDF 2.81 MB
Uni-Probe LB 491 en PDF 1.51 MB
Format Size
ATEX LB 490-TS, LB 491 SuperSENS en PDF 1.89 MB
CCOE LB 490-TS, LB 491 SuperSENS en PDF 243.11 KB
CCOE Zertifikat LB 49x en PDF 243.11 KB
CSA Zertifikat LB 49x en PDF 383.09 KB
FM LB 490-TS, LB 491 SuperSENS en PDF 244.5 KB
Uni-Probe ATEX Certificat LB49x en PDF 1.63 MB
Uni-Probe FM Certificat LB49x en PDF 63.96 KB
Operation Manual
Format Size
LB 491 Uni-Probe en PDF 31.36 MB
Product Information
Format Size
Level & Density Measurement for -50°C (-58°F) de, en PDF 2.26 MB
Uni-Probe User Interfaces en PPT 511 KB
Software Tool
Format Size
LB 490 & LB 491 DTM for HART de, en ZIP 18.78 MB
LB 491 device description for Foundation Fieldbus with capability file de, en ZIP 79.94 KB
LB 491 device description for HART for Siemens Simatic PDM Version 6.0 de, en RAR 55.09 KB
LB 491 device description for HART-communicator de, en ZIP 84.23 KB
LB 491 device description for Profibus PA with GSD file de, en ZIP 116.76 KB
Technical Information
Format Size
LB 491 Uni-Probe de, en PDF 1.07 MB