VPG BHL Nobel AST 3 User manual

Analogue Signal Transmitter AST 3
Contents
1. Introduction
Versions ............... 1-1
Functions .............. 1-2
Technical data ......... 1-4
2. Installation
General ................ 2-1
Electrical installation 2-1
Presentation panel, AST 3P .
2-4
Operation indicator, AST 3B
2-5
3. Set-up
General ................ 3-1
Quick set-up ........... 3-3
Normal set-up .......... 3-7
Parameters ............. 3-9
4. Calibration
General ................ 4-1
Common calibration param. 4-
2
Data sheet calibration . 4-3
Dead weight calibration 4-4
Table calibration ...... 4-4
5. Operation
General ................ 5-1
Power supply ........... 5-1
Power-up sequence ...... 5-1
Display views in Oper. mode
5-2
Zero setting ........... 5-3
Analogue output ........ 5-3
Level supervision, relays 5-
4
6. Communication
Communication interface 6-1
Line termination ....... 6-1
Transmission principles. 6-1
Modbus ................. 6-2
Register descr. -Process
param. ................. 6-6
I/O bit (coil) description .
6-11
Exception responses ... 6-12
Set-up registers ...... 6-13
External display ...... 6-14
7. Troubleshooting
General ................ 7-1
Error codes ............ 7-1
Temporary comm. for AST 3B .
7-6
Appendices
Set-up list for AST 3 App. 1
Declaration of Conformity...
App. 2

Technical Manual

Analogue Signal Transmitter AST 3
1-1
1. Introduction
AST 3 is a high performance signal transmitter, designed for
industrial measuring by means of strain gauge transducers.
The compact module is easily installed on a DIN-rail or a
flat surface.
By serial communication a number of AST 3 modules can be
combined to form a network with a common control unit.
Transducer excitation is included in the transmitter module
and the analogue transducer signal is converted to a digital
signal with very high resolution. By parameter controlled
calculations an internal measurement value is produced, which
can be converted to a current or voltage signal at the
analogue output.
The measurement value can also be transmitted to the control
unit, or to an external display unit.
Level supervision at two levels can be performed and the
status is transmitted
over the serial communication.
All AST 3 inputs and outputs are galvanically isolated from each
other and from
the power supply for the unit.
Versions
AST 3 is available in two versions, both including the same
measuring functions and an analogue output:
AST 3B is designed for remote use. An external control unit
is needed
for set-up of parameter values, and it can also be used for
presentation of
the measurement value.
In AST 3B a green LED is visible through a hole in the
panel, indicating
the operating state of the unit.
In AST 3P components are added to make also local use
possible. A front panel with command keys and a
display window allows local parameter
set-up and display of both parameter and measurement
values at the transmitter module. For AST 3P operating
or error conditions are shown at the display window
(the internal LED is not visible).
AST 3P also includes two output relays for indication
or control duties.

Technical Manual
1-2
Functions
Measuring with strain gauge transducers. The output signal
and the sense (representing the excitation voltage) are
measured at the transducer by four wires to avoid influence
from voltage drop in the connection cable.
Excitation to the transducer, from AST 3 or from an external
DC-power supply, is provided over separate wires.
A shielded 6-wire cable must be used to connect AST 3 to a
distant transducer.
A/D conversion. The analogue signal-to-sense ratio from the
transducer is converted to a digital value and filtered to give
an internal transducer signal representation with high
resolution of the load on the transducer.
Calculation. Influenced by calibration data, the internal
transducer signal is converted to a digital measurement value,
the weight value, that can be presented at the local display
window and at the control unit.
Analogue output. The calculated weight value is also converted
into an analogue output signal, e.g. for presentation on an
external display. Current or voltage output can be selected. The
analogue output can also be forced to produce a selected, fixed
current or voltage signal.
Error supervision. The error supervision is checking for
electrical errors, invalid parameter values, and signals out
of valid limits. As long as no error is detected,
the signal ‘In process’ is present. If an error is detected an
error message will be displayed and the signal ‘In process’
Figure 1. The Analogue Signal Transmitter AST 3 converts analogue
transducer signals
into precise measurement values for use in industrial processes.

Analogue Signal Transmitter AST 3
1-3
will be off, the relays will be deactivated, and the analogue
output signal will be set to 0V / 0mA.

Technical Manual
1-4
Levels. Two level comparators in AST 3 can be set to switch at
defined levels
for selected signals, reporting the status of the signals to the
control unit.
In AST 3P two switching relays are included. They can be set to
indicate
the status of the level comparators or the status of the signal
‘In process’.
Serial communication. In AST 3 the serial interface RS-485,
on 2-wires or
4-wires, is used for communication with the control unit.
Set-up and calibration parameters, weight value, level
status, error status etc. is transmitted via
the Modbus protocol.
If the serial interface is not used for control unit
communication, it can be used to transmit the weight value
to external digital equipment.
Instrument modes. At power-on the unit enters the Start-up
mode, displaying its identity while internal tests are
performed.
Then it may enter the Wait for start mode (selected by a
parameter), waiting for a start command from the operator.
After completed start-up, the AST 3 unit is normally
working in Operating mode, continuously presenting the
weight value (or other selected information).
If editing of set-up parameters should be performed, AST 3
must be switched over to Set-up mode.
If an error is detected, AST 3 will automatically switch
over to Error mode, displaying an error message.
As AST 3 is in Set-up mode or Error mode, normal instrument
operation is disabled, the relays are deactivated, and the
analogue output is set to zero.
Parameter setting. In AST 3 set-up parameters are used to
control all operating functions. The parameter values can be
entered as numerical values or selected from a list of
alternatives.
Setting of the parameter values can be performed from a
control unit.
For AST 3P, the front panel keys and display window can also
be used for
the parameter setting.

Analogue Signal Transmitter AST 3
1-5
Presentation. AST 3 can present parameter values and measured
or calculated signal values at a control unit, and for AST 3P
at the panel display.
The measurement value is also presented by the analogue output
signal.
Controlunit
AST3B
AST3P
PC
AST3P External
display
RS-485
RS-485
Figure 2. The AST 3 versions can utilise serial communication
to carry out different operational tasks.

Technical Manual
1-6
Technical data
Transducer input
Transducers Max 8, 350 ohms each. Total load >45 ohms.
Excitation Depending on the number of transducers
connected:
8.8 VDC 5 % with 1 transd. 8.7 VDC 5 %
with 2 transd.
8.5 VDC 5 % with 3 transd. 7.7 VDC 5 %
with 4 transd.
6.5 VDC 5 % with 6 transd. 5.5 VDC 5 %
with 8 transd.
Signal input 3.3 mV/V.
Sense input 1.5 –10 VDC.
A/D conversion 23 bits (8 300 000 counts). Patented design.
Analogue output
Bipolar voltage or current.
Voltage 0–10 VDC or +/-10 VDC over >500 ohms.
Current 0–20 mA, +/-20 mA, 4–20 mA, -12–20 mA in <500
ohms.
Filter 0.05 to 75 Hz, selectable bandwidth.
Resolution 16 bits (65 000 counts).
Non-linearity <0.01 % of range.
Zero drift <0.005 % of range/C.
Gain drift <0.003 % of actual value/°C.
Serial output
Can be used for control unit communication (Modbus) or external
display.
Interface RS-485, 2-wires or 4-wires.
Baud rate Up to 115.2 kbaud.
Data format Modbus RTU protocol for control unit
communication.
30
735
75
100
110
5
60
85
Mountingholes,
2x4mmdia.
Thesnapfastenerfor
DINrailcanbeopened
withafinescrewdriver.
Figure 3. Mechanical dimensions for AST 3.

Analogue Signal Transmitter AST 3
1-7
Filter 0.05 to 75 Hz, selectable bandwidth.
Non-linearity <0.005 % of range.
Zero drift <0.0002 % of 3.3 mV/V /C.
Gain drift <0.0015 % of actual value/°C.