SCIENCE LCTA User manual
Instruction Manual
Model LCTA
Load Cell Trip/Relay Output Module
Version; 1.0
Release Date: 11/9/2012
Page 1
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
Contents
Description Page
Introduction & Overview 2
Connection & Wiring Details 2
Scaling the voltage output, by applying a known load 3
Scaling the voltage output, using the shunt calibration switch 3, 4
Adjusting the Trip point values 4
Mechanical mounting details 5
Product Specification 6
Page 2
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
Introduction & Overview
The LCTA has been developed to provide relay/trip outputs from a conventional bridge type load cell or
other strain gauge based sensor.
There are two trip/relay outputs available, as well as a voltage output. For further details on their
capabilities, please refer to the specification at the back of this manual.
The principle of operation is that the relay trip levels are set, referenced to the output voltage across pins
15 and 16 on the amplifier (referred to as the voltage output). Once the voltage output has been scaled,
the trip levels can be set, by measuring the voltage at the two test points.
The voltage output can either be scaled by applying known loads, or by using the calibration switch. The
latter is the simplest option; which can be used in conjunction with any load cells supplied with a shunt
calibration output value.
To be able to scale and configure the amplifier, you will need a screwdriver to adjust the potentiometers
and a DVM or multimeter to monitor the output from the amplifier, whilst adjustments are made.
Connection & Wiring Details
Page 3
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
Scaling the voltage output, by applying a known load
With the load cell connected and unloaded, switch on the voltage supply to the amplifier. For best results,
allow 15 minutes for the amplifier to stabilise. Once stabilised follow the steps below:-
(1) Connect your DVM, positive lead to SIGNAL TEST POINT, and the negative lead to the 0vdc field
terminal (terminal 16).
(2) Adjust the ZERO (Z) potentiometer until your DVM shows 0.00V.
(3) Apply your known load
(4) Calculate the required voltage output signal generated with your known load applied, by using the
equation below;
5
Example
You have a load cell rated at 50te and with your applied known load of
20te
5 20
50
5 0.4
.
(5) Based on the example provided above, Adjust the COARSE GAIN and the FINE GAIN
potentiometers until your DVM shows 2.00V.
(6) The amplifier will now be scaled to give you a 0-5V output from zero to the full rated load of your
load cell.
The CAL injects a dummy signal to the LCTA, which simulates a load being applied to the load cell. This
can be used at any point in the future to ensure correct operation of the system.
Scaling the voltage output, using the shunt calibration switch
With the load cell connected and unloaded, switch on the voltage supply to the amplifier. For best results,
allow 15 minutes for the amplifier to stabilise. Once stabilised follow the steps below:-
(1) Connect your DVM, positive lead to SIGNAL TEST POINT, and the negative lead to the 0vdc field
terminal (terminal 16).
(2) Adjust the ZERO (Z) potentiometer until your DVM shows 0.00V.
(3) Slide the CAL switch ON (toward the edge of the board). You should allow 2-3 seconds to allow
the output to stabilise, due to internal electronic damping.
(4) Calculate the required voltage output signal generated by switching the 100kohm calibration
resistor, by using the equation below;
Page 4
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
5
Example
You have a load cell rated at 50te and the calibration certificate shows
the equivalent output for the cal figure to be 40.5te.
5 40.5
50
5 0.81
.
(5) Based on the example provided above, Adjust the COARSE GAIN and the FINE GAIN
potentiometers until your DVM shows 4.05V.
(6) The amplifier will now be scaled to give you a 0-5V output from zero to the full rated load of your
load cell.
(7) Switch off the CAL (toward centre of the board) and recheck the zero. Repeat the above steps
until you are satisfied with the scaling accuracy.
The CAL injects a dummy signal to the LCTA, which simulates a load being applied to the load cell. This
can be used at any point in the future to ensure correct operation of the system.
Adjusting the Trip point values
The trip outputs consist of two independently adjustable changeover relays with volts-free contacts. Each
relay remains de-energised, with its COM terminal connected to its NC pin, until the signal level exceeds
the respective trip level. At this point, the relay energises and the COM terminal is instead connected to
the NO pin.
(1) Connect your DVM, positive lead to TRIP 1 TEST POINT, and the negative lead to the 0vdc field
terminal (terminal 16).
(2) Calculate the required trip 1 test point reference voltage required for trip 1, by using the equation
below:-
1 5 1
Example
You have a load cell rated at 50te and you want Trip 1 to activate at a trip
load value of 45te
1 5 45
50
1 5 0.90
.
(3) Based on the example provided above, adjust the TRIP 1 SET potentiometer until your DVM
reads 4.50V
(4) You have now set TRIP 1 correctly. Repeat the same procedure for Trip 2, with you DVM positive
lead connected to TRIP 2 TEST POINT, adjusting TRIP 2 SET.
Page 5
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
Mechanical Mounting Details
Page 6
LCM Systems Ltd
Unit 15, Newport Business Park, Barry Way
Newport, Isle of Wight, PO30 5GY, United Kingdom
Tel: +44 (0) 1983 249264 Fax: +44 (0) 1983 249266
Product Specifications
Electrical/Performance
Power Supply: 11.5vdc to 24vdc
(48vac external DIN Rail mounting power supply also available)
Power Supply Current: 80mA max. with one 350ohm load cell connected, with both trips active
160mA max for four 350ohm load cell connected, with both trips active
Output: Dual volt free SPCO trip relays
0-5vdc analogue output
Trip Adjustment Range: 0% to 125% FR
Trip Switching Current: 10A at 230vac
10A at 24vdc
Trip Hysteresis: <1%FR
Load Cell Excitation Voltage: 9vdc typically
Load Cell Bridge Resistance: 85ohms minimum
Load Cell Sensitivity: 0.4 to 4mV/V (to provide 0-5vdc output)
Gain Adjustment: Coarse Potentiometer -99% FR
Fine Potentiometer ±4% FR
Offset Adjustment: ±23% FR
Minimum 0-5v Load Resistance: 600ohms
Bandwidth: 3.5HZ
Zero Temperature Coefficient: <±0.01 %/°C with 1.5mV/V input
Span Temperature Coefficient: <±0.01 %/°C with 1.5mV/V input
Linearity: <±0.005 %FR
Environmental
Operating Temperature: -20 to +50°C
Storage Temperature: -40 to +70°C
Humidity: 95% RH max.
Environmental Sealing: See case options below
Mechanical
Electrical Connections: Field Screw Terminals – 2.5mm rising clamp
Cable Access: Via M12 cable glands
Case Options: IP66 fibreglass enclosure (standard)
IP66 Painted Diecast Aluminium
IP40 Din Rail Mounting Open Frame
Controls
Gain Adjustment: Coarse Gain - 25 turn potentiometer
Fine Gain - 25 turn potentiometer
Offset/Zero Adjustment: Zero Offset - 25 turn potentiometer
Trip Point Adjustment: Trip 1 - 25 turn potentiometer
Trip 2 - 25 turn potentiometer
Shunt Calibration: Single switch, switching 100kohm 15ppm resistor
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