Sensia CALDON LEFM CheckPlus-C User manual

Manual IB0919 Rev. 5
CALDON®ULTRASONICS
LEFM®CheckPlus-C
Ultrasonic Flowmeter
Transmitter and Meter Body
User Manual

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Caldon is a trademark of Sensia LLC 2021.
LEFM is a registered trademark of Sensia LLC 2021.
Modbus is a registered trademark of Modbus Organization, Inc.
Copyright © 2021 Sensia LLC. All information contained in this publication is confidential and
proprietary property of Sensia. Any reproduction or use of these instructions, drawings, or
photographs without the express written permission of an officer of Sensia is forbidden.
All Rights Reserved.
Printed in the United States of America
Manual No. IB0919 Rev. 5
February 2014
RECEIPT OF EQUIPMENT
Prior to uncrating, check outside packing case for visible damage. Notify local carrier at once if
damage is present. Inspect unit for damaged or missing parts. Follow up with a written report to:
Sensia LLC
200 Westlake Park Blvd
Houston, TX 77079
[phone]
sensiaglobal.com

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page i Table of Contents
TABLE OF CONTENTS
INTRODUCTION ..............................................................................................................................1
TERMS USED IN THIS MANUAL................................................................................................2
1.0 EQUIPMENT SPECIFICATION ..........................................................................................3
1.1 LEFM CheckPlus-C Equipment.......................................................................................3
1.1.1 LEFM CheckPlus-C Transmitter........................................................................................... 3
1.1.2 LEFM CheckPlus-C Metering Section.................................................................................. 4
1.2 LEFM CheckPlus-C Transmitter Part Code.....................................................................4
1.2.1 LEFM CheckPlus-C Transmitter........................................................................................... 5
1.2.2 Environment.........................................................................................................................6
2.0 INSTALLATION ......................................................................................................................7
2.1 Transmitter and Terminations...........................................................................................7
2.1.1 Transmitter Mounting........................................................................................................... 7
2.1.2 RS-485 Communication .......................................................................................................8
2.1.3 Grounding/Earthing.............................................................................................................. 8
2.1.4 Digital Outputs.....................................................................................................................8
2.2 Meter Installation Check-Out..........................................................................................15
3.0 OPERATIONAL OVERVIEW.............................................................................................16
3.1 Measuring Velocities.......................................................................................................16
3.2 Measuring Flowrate.........................................................................................................17
3.3 LEFM CheckPlus-C Transmitter....................................................................................18
3.4 Temperature-Density Determination..............................................................................18
3.5 Remote Data Communications.......................................................................................18
4.0 OPERATION...........................................................................................................................19
4.1 Definitions........................................................................................................................19
4.2 Normal Operating Conditions.........................................................................................19
4.3 Display..............................................................................................................................20
4.3.1 Boot up and Normal Operational Screens............................................................................21
4.3.2 Path Level Alarm Display Screens...................................................................................... 24
4.3.3 Meter State Alarm Display Screens.....................................................................................24
4.4 Output Test Mode............................................................................................................26
4.5 Bad Setup File..................................................................................................................26
4.6 Switch Forced Setup........................................................................................................27
5.0 MAINTENANCE ....................................................................................................................28
5.1 Introduction......................................................................................................................28
5.2 General Inspections - Preventative Maintenance Procedures.......................................28
5.2.1 Enclosure Inspection...........................................................................................................28
5.2.2 Internal Electronics Inspection............................................................................................ 29
5.3 Power Supply Voltage Troubleshooting and Maintenance...........................................30
5.4 CTC Troubleshooting and Maintenance ........................................................................31
5.5 MXR Troubleshooting and Maintenance.......................................................................33
5.6 IOB Troubleshooting and Maintenance.........................................................................34

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Table of Contents Page ii February 2014
5.7 Analog Input/Output Verification Procedure.................................................................35
5.7.1 Analog Inputs.....................................................................................................................36
5.7.2 RTD Inputs.........................................................................................................................38
5.7.3 Analog Outputs..................................................................................................................38
5.8 Analog Input Verification ...............................................................................................39
5.9 Analog Output and Pulse Output Verification...............................................................39
5.9.1 Force Output (Analog)........................................................................................................39
5.9.2 Force Output (Pulse)...........................................................................................................39
5.9.3 Changing Digital Output Voltage........................................................................................ 39
5.10 Metering Section and Transducer Cables.......................................................................40
5.10.1 Metering Section Inspection ............................................................................................... 40
5.10.2 Transducer Cable Inspection...............................................................................................40
5.11 Transducers......................................................................................................................41
6.0 TROUBLESHOOTING AND DIAGNOSTICS FOR THE ULTRASONICS..............43
6.1 Diagnostics.......................................................................................................................43
6.2 Alarm Conditions.............................................................................................................43
6.3 Meter Troubleshooting....................................................................................................44
6.3.1 Internal Communication ..................................................................................................... 44
6.3.2 Analog Input ...................................................................................................................... 44
6.3.3 Path Failure........................................................................................................................ 45
6.3.4 Clock Failure...................................................................................................................... 45
6.4 Path Troubleshooting.......................................................................................................45
6.4.1 Path Reject Status...............................................................................................................46
6.4.2 Calculation Error................................................................................................................ 48
6.4.3 Iteration Failure.................................................................................................................. 48
6.4.4 Velocity of Sound Failure................................................................................................... 48
6.4.5 Velocity Outlier.................................................................................................................. 49
6.4.6 Impedance Failure..............................................................................................................49
6.5 Reprogramming the Transmitter.....................................................................................50
6.5.1 Modbus ID and Baud Rate..................................................................................................50
7.0 RECOMMENDED SPARE PARTS....................................................................................51

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 1 Introduction
INTRODUCTION
The Caldon LEFM CheckPlus-C Ultrasonic Flow Transmitter is a highly sophisticated flow measurement
system. It employs the ultrasonic transit time method to measure fluid velocity and flow rate. It contains
advanced signal and data processing circuitry to achieve high accuracy and repeatability. It also contains an
automatic self-checking system to continuously verify that it is performing properly and to initiate warnings
and alarms when unsatisfactory conditions are detected. For ease of troubleshooting, it provides easy to
interpret diagnostic information via Modbus®.
It is recommended that before performing system verification and repair procedures, personnel receive
general training from Cameron. Contact Cameron for information on training programs.
Cameron is a manufacturer of high quality instrumentation and control products, selling direct from its
Pittsburgh based factory to customers in the U.S. and through agents and representatives abroad. A
complete range of support services are offered. For additional information or assistance on the application,
operation, or servicing of the LEFM CheckPlus-C, visit www.c-a-m.com.

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Important Safety Information Page 2 February 2014
CAUTION
CAUTION
WARNING
HOT
SURFACE
Important Safety Information
OPERATORS SHOULD NOT REQUIRE ACCESS TO THE INTERIOR OF THE ELECTRONICS.
ONLY QUALIFIED PERSONNEL SHOULD SERVICE THE ELECTRONICS. DO NOT ATTEMPT
TO DISASSEMBLE THE INSTRUMENT OR OTHERWISE SERVICE THE INSTRUMENT
UNLESS YOU ARE A TRAINED MAINTENANCE TECHNICIAN.
If the equipment is used in a manner not specified by Cameron, the protection provided by
the equipment’s safety features may be impaired. Cameron is not responsible for damages
or injuries sustained as a result of inappropriate use.
Before performing system verification and repair procedures, contact Cameron’s Measurement Systems
division, Caldon Ultrasonics.
For additional information or assistance on the application, operation or servicing, write or call the
Cameron office nearest you or visit www.c-a-m.com
Terms Used in this Manual
This symbol identifies information about practices or circumstances that can lead to
personal injury or death, property damage, or economic loss.
This symbol indicates actions or procedures which if not performed correctly may
lead to personal injury or incorrect function of the instrument or connected
equipment.
This symbol indicates a particular surface maybe hot and touching this surface may
lead to personal injury.
Note – Indicates actions or procedures which may affect instrument operation or may lead to an instrument
response which is not planned.

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 3 Equipment Specification
1.0 EQUIPMENT SPECIFICATION
1.1 LEFM CheckPlus-C Equipment
The LEFM CheckPlus-C Flow Measurement System consists of three major pieces of equipment:
LEFM CheckPlus-C CPU (covered in manual IB1002)
LEFM CheckPlus-C Transmitter
LEFM CheckPlus-C Meter Body
The LEFM CheckPlus-C Meter Body includes the following:
Transducers
High-Temperature Nickel Transducer Cables (to run between the Transmitter or Junction Box and
the Meter Body)
Low Smoke Transducer Cables (if a junction box is installed, between the junction box and
Transmitter)
Temperature Sensors (two RTDs per Meter Body)
Pressure Transmitters (optional)
1.1.1 LEFM CheckPlus-C Transmitter
The LEFM CheckPlus-C Transmitter is a wall mount unit with the following special features:
Standard Outputs:
Flow Pulse (0-5 V standard, 0-12 V optional); the meter K factor is programmable (minimum
frequency 3 Hz)
RS-485 Serial Output (Modbus)
Standard Analog Inputs:
Temperature 100 Ohm PT RTD, α = 0.00385
Pressure (0,4-20 mA)
Optional Analog Outputs (Select 1 if used):
Density (0,4-20 mA)
Specific Gravity (0,4-20 mA)
Temperature (0,4-20 mA)
Velocity of Sound – (0,4-20 mA)
Flow – (0,4-20 mA)
Display Screen indicating:
Volume Flow or Mass Flow
Temperature
Acoustic Path Status
System Density
Totalized Flow

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Equipment Specification Page 4 February 2014
1.1.2 LEFM CheckPlus-C Metering Section
The metering section contains the acoustic transducers that transmit and receive the ultrasonic pulses that
pass through the fluid.
The metering section is configured with eight pairs of ultrasonic transducers. The LEFM CheckPlus-C
Transmitter is programmed with the dimensions of the metering section (effective area, linear distance
between transducers, transducer path angle with respect to pipe centerline, etc.) in order to calculate flow
from acoustic measurements made within the metering section.
The transmitter also reflects the transducer configuration, including the number of transducer measurement
pairs and spacing of the pairs. The metering section is designed such that eight acoustic pairs of transducers
are spaced to measure axial flow on specific chords across the diameter of the pipe at an angle to the flow
direction. The spacing typically accommodates the Gaussian Method of flow integration.
The transducer modules contain piezoelectric crystals. Each transducer transmits and receives ultrasonic
pulses (typically 1.6 MHz). The LEFM CheckPlus-C Transmitter operating frequency is matched to the
transducers. Transducer cables are used to route electronic signals between the LEFM CheckPlus-C
Transmitter and the transducers.
1.2 LEFM CheckPlus-C Transmitter Part Code
As a member of the Cameron product family, each LEFM CheckPlus-C Transmitter has a part code that
completely defines the construction and features of the flow meter. Table 1-1 defines the part code.
Part Number Power Supply Frequency Paths Enclosure
Material
9A-203B050G01 120 VAC 1.6 MHz 4 Path Stainless Steel
9A-203B050G02 240 VAC 1.6 MHz 4 Path Stainless Steel
9A-203B050G03 120 VAC 1.6 MHz 4 Path Carbon Steel
9A-203B050G04 240 VAC 1.6 MHz 4 Path Carbon Steel
Table 1-1 LEFM CheckPlus-C Transmitter Part Code

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 5 Equipment Specification
LEFM CheckPlus-C Specifications
1.2.1 LEFM CheckPlus-C Transmitter
Material:
NEMA 4X Stainless Steel
NEMA 4 Painted Carbon Steel
Wall Mount
Net Weight: 35 lbs. (15.9 kg)
(See Figure 2-1 for dimensions)
Power Requirements
Voltage Supply Required: 120 VAC, 50/60 Hz or,
230 VAC, 50/60 Hz
Current Draw: 120 VAC – 0.8 Amps
230 VAC – 0.6 Amps
Power Consumption: 12W (80W with heaters active)
Cable Lengths
Standard: 25 feet (approximately 7.6 meters); lengths up to 100 feet (31
meters) can be ordered
Extended Range: Special cables can be used for runs up to 1000 feet (310 meters).
Contact the Cameron Engineering department to discuss the
needs of the application.
Pulse Outputs/Communications
Pulse Output: 0-5 V (standard) or 0-12 V (optional)
Alarm Status: 5V or 12V @ 20 mA Normal, 0V Alarm
Serial Communications: RS-485 Modbus Protocol (see Cameron Modbus Specification)
Modbus TCP (Ethernet)
Analog Output: 0,4-20 mA (max load 650 Ohms) X 2
Analog Inputs: 0,4-20 mA and RTD

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Equipment Specification Page 6 February 2014
CAUTION
1.2.2 Environment
Indoor or Outdoor Use
Altitudes up to 3000 meters
Pollution – Degree 2
Power Supply ±10% of nominal voltages
Storage Temperature
Transducer Cable: N/A
Transmitter: -70°F (-57°C) to 158°F (70°C)
Operating Temperatures
Transmitter: -40°F (-40°C) to 140°F (60°C)
Transducer Cable (High Temp): -148°F (-100°C) to 500°F (260°C)
Transducer Cable (Low Smoke): -22°F (-30°C) to 176°F (80°C)
Confirm that all other cables entering the transmitter (e.g., power, analog input, analog
output, RS485 etc) that are supplied by the site installation team, are rated to 80 deg C. This
rating allows cables to comply with the full temperature range of the transmitter.
Relative Humidity
Transmitter: 0 – 95% Relative Humidity (Internal)
0 – 100% Relative Humidity (External)
EMI According to EPRI standard TR-10323 Rev 3
EN Standards EN61326-1 (EN-61000)

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 7 Installation
2.0 INSTALLATION
The exact physical properties, acoustic properties, and calibration of the metering section are programmed
into the transmitter as part of the commissioning activities. When installing multiple units ensure that
the transmitter is properly associated with the intended metering section and measurement plane.
2.1 Transmitter and Terminations
The LEFM CheckPlus-C meter is designed to be used under a wide variety of environmental conditions.
Durable construction permits conventional installation practices. The transmitter should be installed in an
environment consistent with the ratings of the enclosure. All wiring to and from the transmitter must be put
in grounded metal conduit or equivalent. Mounting must use the mounting points indicated in Figure 2-1.
No ventilation is required, other than that is necessary to meet the ambient temperature requirements.
2.1.1 Transmitter Mounting
For installation, simply uncrate the delivered transmitter (please note the weight of your transmitter in
Section 1.2.1 for proper handling). Use the indicated mounting points for mounting the units. Select
bolts/hardware appropriate for the unit’s weight. Consider site seismic requirements.
Use 5/16 inch bolts/hardware (or equal) on at least the 4 top and 4 bottom mounting points for the
LEFM CheckPlus-C Transmitter and torque to 18 ft/lbs.
The mounting hardware must be capable of handling 4 times the transmitter’s weight or
approximately 140 lbs (63.6 kg). This should be verified by the site installation team (EN61010).
The transmitter should be mounted at a convenient working height. (The recommended height is the
bottom of the transmitter at about 4 feet (1.2 meters) from the floor.)

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Installation Page 8 February 2014
2.1.2 Field Terminations
The wiring should be routed to the transmitter in shielded conduit that meets site environment
specifications. All terminations should be made according to Table 2-1 through Table 2-6.
For full environmental temperature range, all wiring (conductors) into and out of the transmitter should be
rated as follows:
Temperature range - minimum of 176°F (80°C).
All supply wiring must be rated to 300 volts AC (18 AWG).
Equipment must be installed by a licensed electrician, in accordance with NEC/CEC and local
codes.
As a minimum, a disconnect switch should be installed before and near the transmitter. The
external disconnect device must be an approved device rated for the supply voltages and is rated to 3
Amps for 120 VAC or 240 VAC and provide a minimum of 3.0 mm spacing. This remote
disconnect should be marked as the disconnect to the Transmitter.
Figure 2-1 illustrates the conduit connections for the LEFM CheckPlus-C Transmitter and the transmitter
layout. Transducer termination guide is defined in Table 2-1. Metering section transducers are defined in
acoustic pairs, path 1 through path 4, and designated as upstream or downstream with respect to typical
flow direction. Each transducer has a positive and negative lead and a shield wire.
2.1.2 RS-485 Communication
Serial communications is RS-485. Table 2-6 shows pin out for serial communications. The system also has
the option for Ethernet connectivity using two RJ45 jacks. Each of the communication ports (Channel 1 and
Channel 2) can be configured for either serial or Ethernet using the switches 1 and 2 located on the
datalogger board.
2.1.3 Grounding/Earthing
The transmitter has grounding/earthing points available. Site guidelines are to be followed regarding
grounding/earthing. Transducer cable shields are to be grounded in the transmitter, but not at the
transducers. Shielding through the transmitter terminal blocks avoids undesirable ground loops. Note that
some installations may use transformers to match other vendor’s transducers (single ended transducers). In
these installations, the shield termination may not be landed.
2.1.4 Digital Outputs
The LEFM CheckPlus-C Transmitter is a bidirectional meter and has two digital output options that
indicate direction. The first is quadrature pulse output to indicate direction of flow (reference Table 2-4).
Quadrature output uses two pulse outputs (A and B). Pulse output A leading pulse output B by 90° indicates
forward flow while pulse output B leading pulse output A by 90° indicates reverse flow with respect to the
flow arrow of the nameplate. The second is a level indication that is driven by direction (output "Hi" for
positive flow and "Lo" for negative flow).

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 9 Installation
Figure 2-1: Transmitter Enclosure (units in inches, [mm])

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Installation Page 10 February 2014
Figure 2-2: Electronics with Door Open
Circuit Breaker – ON to the LEFT, OFF to the RIGHT
On/Off
Breaker
See Figure 2-2A
Transducers
RTD
Analog I/O
RS
-
485
Digital I/O
Power

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 11 Installation
Figure 2-2A – Transmitter Assembly Board
Top View
Power
Supply
Check
± 12Vdc
± 5 Vdc
Jumper
“2” wire – RS485 “4” wire – RS485
E1 (pins 1&2) E1 (pins 3&2)
E2 (pins 1&2) E2 (pins 3&2)
Indicates Unit
Operating

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Installation Page 12 February 2014
Table 2-1: LEFM CheckPlus-C Transducer Terminations
Transducer Cable Identification Transmitter Termination
Wire Name Device Terminal
1 UP + TB1 1 Shield TB1 2
- TB1 3
2UP + TB1 4 Shield TB1 5
- TB1 6
3 UP + TB1 7 Shield TB1 8
- TB1 9
4 UP + TB1 10 Shield TB1 11
- TB1 12
1 DN + TB1 13 Shield TB1 14
- TB1 15
2 DN + TB1 16 Shield TB1 17
- TB1 18
3 DN + TB1 19 Shield TB1 20
- TB1 21
4 DN + TB1 22 Shield TB1 23
- TB1 24
+ TB2 1
5 UP Shield TB2 2
- TB2 3
+ TB2 4
6 UP Shield TB2 5
- TB2 6
+ TB2 7
7 UP Shield TB2 8
- TB2 9
+ TB2 10
8 UP Shield TB2 11
- TB2 12
+ TB2 13
5 DN Shield TB2 14
- TB2 15
+ TB2 16
6 DN Shield TB2 17
- TB2 18
+ TB2 19
7 DN Shield TB2 20
- TB2 21
+ TB2 22
8 DN Shield TB2 23
- TB2 24

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 13 Installation
Analog Input
Source RTD Connections 0, 4-20mA Connection
Description Terminus Description Terminus
Analog Input 1 0, 4-20mA + TB4-1 0, 4-20mA - TB4-2
Shield TD4-3
Analog Input 2 0, 4-20mA + TB4-7 0, 4-20mA - TB4-8
Shield TD4-9
Fluid Temperature
RTD + TB3-1
RTD + TB3-2
RTD - TB3-3
RTD - TB3-4
Shield TB3-5
Table 2-2: Analog Input Customer Connection Locations
(Located on Backplane)
Note: TP4 on the IOB can be used to verify analog input value
Typical
Analog Output* Signal Description Terminus
Analog Output 1
Flow (0)
4,0-20 mA + (high) TB4-4
4,0-20 mA– (low) TB4-5
Shield TB4-6
Analog Output 2
Flow (38)
4,0-20 mA + (high) TB4-10
4,0-20 mA– (low) TB4-11
Shield TB4-12
Table 2-3: Analog Output Customer Connection Locations (Located on Backplane)
*Note: Other variables can be mapped to the analog outputs (reference Cameron Modbus manual).
Name Signal Description Terminus
Pulse A +V, Indicates forward flow TB6-1
GND5 Ground TB6-2
Pulse B or
Direction
+V, Pulse 90 degrees phase shift to Pulse A
If phase lags (positive flow) - if phase leads (negative flow)
Direction: +V indicates reverse flow, 0 Indicates positive flow TB6-3
GND5 Ground TB6-4
Status +0V, Indicates alarm condition
+V, Indicates normal operation TB6-5
GND5 Ground TB6-6
Table 2-4: Pulse and Digital Output Wiring
Note: +V can be jumpered to 5 volts or 12 volts

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Installation Page 14 February 2014
Power
Connectivity Description Terminus
120 VAC
LINE Power-1
Neutral Power-2
Ground/Earth Power-3
24 VDC
+24 VDC Power-1
24 VDC Return Power-2
Ground/Earth Power-3
240 VAC
LINE 1 Power-1
LINE 2 Power-2
Ground/Earth Power-3
Table 2-5: Power Connections
(Only one type of power should be connected)
Port
Name Termination RS-485 Full Duplex* E1, E2 Jumpered 2-3 RS-485 Half Duplex* E1, E2 Jumpered 1-2
COM1
BPL-TB5-1 A, Noninverting Receive (+Rx)
BPL-TB5-2 B, Inverting Receive (-Rx)
BPL-TB5-3 Isolated Ground
BPL-TB5-4 Y, Noninverting Transmit (+Tx) Y, Noninverting Transmit/Receive (+Data)
BPL-TB5-5 Z, Inverting Transmit (-Tx) Z, Inverting Transmit/Receive (-Data)
BPL-TB5-6 Chassis Ground
COM2
BPL-TB5-7 A, Noninverting Receive (+Rx)
BPL-TB5-8 B, Inverting Receive (-Rx)
BPL-TB5-9 Ground
BPL-TB5-10 Y, Noninverting Transmit (+Tx) Y, Noninverting Transmit/Receive (+Data)
BPL-TB5-11 Z, Inverting Transmit (-Tx) Z, Inverting Transmit/Receive (-Data)
BPL-TB5-12 Chassis Ground
Table 2-6: RS-485 Serial Communications
* Jumpering E1 (COM1) and E2 (COM2) on the transmitter backplane board to positions 1-2 selects half
duplex mode. Jumpering E1 (COM1) and E2 (COM2) on the transmitter backplane board to positions 2-3
selects full duplex mode (reference Figure 2-2A).

LEFM CheckPlus-C Transmitter User Manual IB0919 Rev. 5
February 2014 Page 15 Installation
CAUTION
2.2 Meter Installation Check-Out
The following steps are recommended to checkout a meter’s installation. See Section 5 and 6for
troubleshooting and maintenance. Also reference Cameron procedure EFP-68.
Step 1: Verify all field terminations have proper continuity and isolation from each other and earth. Verify
connections are good with respect to insulation.
Step 2: Verify electronics turn on when CB1 (input power breaker) is closed (Display lights up on front
panel). Reference Figure 2-2.
The circuit breaker is ON (power applied) when the switch is to the LEFT and OFF
(electronics off) when the switch is to the RIGHT.
Step 3: Verify Modbus communications (Use Caldon LEFM Link 2G software or plant computer to
communicate). Verify meter operation according to Section 5.
Step 4: Verify Analog Output, preferably using LEFM Link to force outputs (current and pulses). Forcing
outputs verifies connections to site instruments. Verify observed forced outputs are within 0.1% on current
and 0.01% on pulse frequency. Return meter to normal operation.
Step 5: If pipe is full of liquid, verify acoustic signals have Rejects < 2% and SNR (signal to noise ratio) >
40:1. Verify standard deviations of Paths 1 and 4 are less than 6% (for flowing conditions) and verify the
standard deviations of Paths 2 and 3 are less than 4% (for flowing conditions). See Section 5.0.

IB0919 Rev. 5 LEFM CheckPlus-C Transmitter User Manual
Operational Overview Page 16 February 2014
3.0 OPERATIONAL OVERVIEW
3.1 Measuring Velocities
LEFM Ultrasonic Flow Meters use pairs of ultrasonic transducers to send acoustic pulses to one another
along a measurement path. The measurement path is at an angle to the fluid flow. The acoustic pulse’s
transit time depends upon both the velocity of sound (VOS) in the fluid and the velocity of the fluid along
the path. The transit time will be shorter for pulses, which travel downstream with the flow, than for the
pulses which travel upstream against the flow.
Pf
PVC 

D
T
Pf
PVC 

U
T
where TD= downstream transit time
TU= upstream transit time
ℓp= path length
Cf= velocity of sound in fluid
Vp= flow velocity along the ultrasonic path
V = flow velocity along pipe axis
Figure 3-1: Flow Velocities along the Ultrasonic Path and the Pipe Axis
Downstream Transducer
Upstream Transducer
ℓP
VPV
