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Model: AHM Users Manual
Portable Battery Powered Load Cell Indicator
TEDs Enabled
TEDS
enabled
Load Cell Central follows a policy of continuous improvement and reserves the right to change specifications without notice. © 2015
Load Cell Central
28175 Route 220
Milan, PA 18831
Web: www.800loadcel.com
Email: [email protected]
Toll Free: 1-800-562-3235
Ph: 1-570-731-7048
Fax: 1-570-731-7054
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Load Cell Central
AHM User Manual
What is TEDS?
"Plug and play sensor hardware and software make configuring a smart TEDS sensor as easy as plugging a mouse into a PC. The technology has greatly improved efficiency and productivity by
completely eliminating manual sensor configuration."
Basic concept
TEDS is at the heart of the new universally accepted IEEE 1451.4 standard for delivering Plug and Play capabilities to analogue measurement and test instruments. In essence, information in a Transducer
Electronic Data Sheet provides interfacing devices with the critical sensor calibration information in order to perform accurate and precise measurements every time.
TEDS works in a similar way in which USB computer peripherals immediately work as they are connected.
TEDS enabled equipment maybe swapped and changed without recalibration, saving time and money.
TEDS holds information such as a sensor manufacturer, model and serial numbers, and more importantly all the calibration settings determined by the manufacturer.
How it works
Plug and play is a data acquisition technology that can simplify the configuration of automated measuring systems by making a sensor’s unique identification data available electronically. As implemented according to IEEE P1451.4, data in the form of a transducer electronic data sheet (TEDS) is burned on an electrically erasable programmable read-only memory (EEPROM) chip located on the sensor, so when a properly adapted signal conditioner interrogates the sensor, it can interpret the self identification data. This technology provides a great benefit by eliminating the need for paper calibration sheets. In addition, it can simplify labeling and cabling problems, as well as inventory control issues; by letting you burn location data onto the chip when installing a sensor. And because all sensors produced according to the standard will carry the same basic identically formatted self-identification information, you will be able to mix and match sensors and applicable signal conditioners across manufacturers.
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Advantages
Plug and play sensors are revolutionizing measurement and automation. With Transducer Electronic Data
Sheets (TEDS), your data acquisition system can detect and automatically configure sensors. This technology provides:
•
Reduced configuration time by eliminating manual data entry
•
Better sensor tracking by storing data sheets electronically
•
Improved accuracy by providing detailed calibration information
•
Simplified asset management by eliminating paper data sheets
•
Reliable sensor location by identifying individual sensors electronically
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AHM User Manual
Introduction
The AHM Portable Strain Display Load Cell/Force transducer readout is a microprocessor based portable instrument designed to interface with any full bridge sensor with an output sensitivity of up to 50mV/V.
Bridge resistances from 85Ω upwards can be used with the AHM.
Configuration and calibration of the AHM is achieved using the front panel push buttons to navigate through a very simple menu structure.
User functions available on the AHM include:-
Range Selection
Display Hold/Freeze
Gross/Net indication selection
Peak Hold selection
Trough Hold selection
Shunt Cal check
The AHM is powered by two internal non-rechargeable AA alkaline batteries.
User Operation
Full 7 digit LCD display
6 Push Buttons used for normal operation and for configuration
Load Cell Central AHM User Manual
Operation Annunciators
Unit Labels
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Electrical Connection Information
Sensor Connections
The standard sensor connection is a 5 pin 723 series Binder connector. The wiring for this is detailed below:-
PIN 1
PIN 2
PIN 3
PIN 4
PIN 5
+ve Excitation
-ve Excitation & TEDS Common
+ve Signal
-ve Signal
TEDS
RS232 Port Connections
If the AHM has been ordered with the optional RS232 output, then this will be available via a 8 pin
723 series Binder connector. The wiring for this is as detailed below:-
PIN 1
PIN 2
PIN 3
Tx
Rx
Gnd
Note: PINS 4 to 8 not connected
Internal Connections
It may be necessary from time to time to know what the internal connections are. For example, if you disturb some of the connections whilst trying to insert the range legends, or if you need to change the internal shunt calibration resistor. These are shown below for reference only:-
Shunt Calibration Resistor
Sensor Connections
RS232 option
J9 TEDs Position
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AHM User Manual
There are six push buttons on the front panel of the AHM, which are available for use in normal operation. Each of these is described below:-
Front Panel Button Function of Button in Normal Operation Mode
To switch the AHM ON or OFF press and hold the button
The RANGE button allows the user to toggle between two independent scales. An annunciator highlights the range that has been selected.
The
HOLD button allows you to hold/freeze the current display value when the button is pressed. Pressing the
HOLD button again releases the display.
The
HOLD annunciator is illuminated when in the HOLD mode, and the display will flash, to alarm further that the user is not viewing instantaneous display values.
The GROSS/NET button, when pressed, allows the user to toggle between displaying the Gross or Net display values. This can be useful in many applications where it is necessary to display the change in display value from a certain part of the measurement range. When in NET mode the NET annunciator is lit. When in
GROSS mode, the NET annunciator is not lit.
The
SHUNT CAL button allows the user to press this at any point in time.
The standard unit shunts a 100kΩ resistor across the negative excitation and negative signal connections. If this is performed at the end of the calibration procedure, then a figure can be noted, so the user can check calibration accuracy or connection integrity. The button has to be held down to operate. When held down the SHUNT CAL annunciator is lit and the display will flash, to alarm further that the user is not viewing instantaneous display values.
When the PEAK button is pressed the display will show the last Peak reading.
To reset the Peak readings press the PEAK and TROUGH buttons simultaneously. When in
PEAK mode the PEAK annunciator will be lit and the display will flash, to alarm further that the user is not viewing instantaneous display values. To turn off Peak mode press the
PEAK button.
When the
TROUGH button is pressed the display will show the last Trough reading. To reset the Trough readings press the
TROUGH and PEAK buttons simultaneously. When in
TROUGH mode the TROUGH annunciator will be lit and the display will flash, to alarm further that the user is not viewing instantaneous display values. To turn off the Trough mode press the
TROUGH button
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Menu Structure
The AHM has two menus, details of which are outlined below:-
A CONFIGURATION MENU, which enables the user to tailor the operation to meet a specific application requirement. The values selected in the CONFIGURATION MENU are completely independent for each range.
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AHM User Manual
A Calibration Menu, which is used to calibrate each of the two ranges with independent scales, as well as setting the display resolution for each range.
SEnS 5.0
SEt rES 0000.000
*
CALibrAt
tedS
LiVE?
tAbLE?
uSE SC?
APPLY LO
APPLY LO dISP LO dISP LO
0000000
0000000
APPLY HI dISP HI dISP HI
0000000 donE
0000000
InPut LO 0000000 dISP LO 0000000 InPut HI 0000000 dISP HI donE
0000000 donE
0000000
SEt OFFS 0000000 donE
CAL VAL?
EnAbLEd?
SEt 9Ain
RETURN TO
NORMAL DISPLAY
MODE
* Note:Only when TEDS is disabled
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Millivolt per Volt Calibration Menu Structure
To access the
millivolt CALIBRATION MENU,
Press and hold and for 10 seconds
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Load Cell Central
AHM User Manual
Configuration Menu
To enter the CONFIGURATION MENU, press and hold and buttons for 3 seconds
Parameter Set-up Information
Press To skip to next menu item
Press To set a new system zero
This allows the user to introduce a fixed offset to the display value. The GROSS and NET values are then displayed with this offset taken into account.
SEt ZEro
Values between
-9999999
and
+9999999
can be entered, using the and arrows to select a digit and the and arrows to increment or decrement the digits. Press to accept the value and move onto the next parameter.
Set Zero may also be set by pressing and at the same time.
Press To skip to next menu item
Press To change the update rate
SEt rAtE
This allows the user to set the display update rate, the options available is the update rate of the display in Hz. Please note that the 25Hz update is only available in PEAK or TROUGH mode.
When you choose to change the update rate you will be prompted whether you want to select
25Hz, if you do not press you will then be prompted to select any of the other values, which in order, are 10Hz, 3Hz, 1Hz, 0.5Hz. to set the update rate for the value you want press
SEt
OUEr
Press To skip to next menu item
Press To set overload alarm
This allows the setting of a visual overload. The value entered is the display value at which the AHM displays
OUErLOAd
.
Values between
-9999999
select a digit and the
and
and
+9999999
can be entered, using the and
arrows to increment or decrement the digits. Press accept the value and move onto the next parameter.
arrows to
to
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10
Parameter
SEt
OPEr
Set-up Information
Press To skip to next menu item
Press To select operation mode
This allows the enabling or disabling of the power save mode, which updates at 1 update per second and pulses the sensor excitation. This results in a lower accuracy (1 part in 20,000).
To enable press
To disable press
AUtO
OFF
Press To skip to next menu item
Press To set auto power off
This enables the setting of an auto power off value. The value entered is in minutes. If no front panel buttons are pressed for the time set here, then the indicator will automatically power off, to conserve battery life.
Values between
05
and
99
can be entered (between
00
and
04
leaves the AHM permanently powered), using the and arrows to select a digit and the and arrows to increment or decrement the digits. Press to accept the value and move onto the next parameter.
rS232
Press To skip this parameter and exit menu
Press To enable the RS232 output
This feature enables you to enable or disable the RS232 output. Further details of the RS232 format are provided further into this manual. The RS232 output is an option that has to be ordered with the AHM. To conserve battery life, it is suggested that the RS232 output is disabled, when it is not required.
To enable press
To disable press
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AHM User Manual
Calibration Menu
To enter the
Calibration Menu, press and hold and buttons for 5 seconds
Parameter Set-up Information
Press To skip to next menu item
Press To change sensor input sensitivity
SEnS 5.0
This allows the calibration engineer to change the sensitivity range of the AHM, when connecting to sensors with a sensitivity of greater than 5mV/V. The AHM is factory set
To select 50mV/V you need to power down the unit and access the internal circuit board.
Move link LK1 and place it onto JP1. Power on the AHM and return to this point of the calibration menu. You will notice that the menu parameter has changed to
SEnS 50.0
, press
to change the sensitivity to 50mV/V and move on to the next parameter.
Press to skip to next menu item
Press to the set the display resolution
This parameter sets the decimal point position for the display and the resolution, i.e. a value of
000.005
would display the reading to 3 decimal places and the readings will change in steps of 0.005.
SEt rES
The decimal point position is moved one place to the right each time you press the and
together.
Any value can be entered for the resolution, using the and the and
and
arrows to increment or decrement the digits. Press value and move onto the next parameter.
arrows to select a digit
to accept the
To save the settings and move on to the next parameter press
THIS MENU IS DISABLED WHEN TEDS IS ENABLED
Press to skip to next menu item.
Press to the enter the calibration routine
CALibrAt
If you have chosen to enter the calibration routine you will be prompted whether you want to select
LiVE
, if you do not press
,
otherwise press . You will then be prompted to select either of the other calibration methods, which in order, are
tAbLE
and
CAL VAL
to select any of the calibration methods press . Otherwise press
For more detailed calibration information, please refer to the calibration section of the manual.
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tedS
ENABLING TEDS DISABLES CALIBRATE MENU
Press to skip this parameter and exit menu
Press to enable or disable TEDS.
If you have chosen to enter the TEDS calibration,
EnAbLEd?
appears.
If you have chosen to enter the TEDS you will be prompted whether you want to select
EnAbLEd?
if you do not press
,
otherwise press . If you have selected enabled, two flashing indicators will appear.
For more detailed TEDS calibration information, please refer to the TEDS section of the manual.
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Load Cell Central
AHM User Manual
Millivolt per Volt Calibration Menu
To enter the
MilliVolt per Volt Calibration Menu, press and hold and buttons for 10 seconds
Parameter Set-up Information
Press To skip to next menu item
Press To change the 5mV/V gain.
5.0 gAIn
Here the factory gain calibration can be changed to a measured value (see Milli-Volt
Calibration Procedure – back end of manual).
Once the derived value has been entered Press to confirm.
Press to skip to next menu item
Press to change the 5mV/V offset.
5.0 OFFS
Here the factory offset value can be changed to a measured value (see Milli-Volt Calibration
Procedure – back end of manual).
Once the derived value has been entered Press to confirm.
THIS CAN ONLY BE SET WHEN USING 50mV/V RANGE
Press To skip to next menu item
Press To change the 50mV/V gain.
50 gAIn
Here the factory gain calibration can be changed to a measured value (see Milli-Volt
Calibration Procedure – back end of manual).
Once the derived value has been entered Press to confirm.
THIS CAN ONLY BE SET WHEN USING 50mV/V RANGE
Press to skip to next menu item
Press to change the 5mV/V offset.
50 OFFS
Here the factory offset value can be changed to a measured value (see Milli-Volt Calibration
Procedure – back end of manual).
Once the derived value has been entered Press to confirm.
Load Cell Central AHM User Manual
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Operation Features
Normal Display Operation
The AHM has a full 7 digit display, which can be scaled using the calibration menu to suit the application it is to be used in. The display can display the instantaneous, peak or trough values. It is also possible to hold the display value (this only operates when not in peak or trough mode).
The display update rate, decimal point position and resolution can be set to suit.
The AHM has two independent ranges. All values set in one range are totally independent from the other.
Switching the AHM On/Off
The AHM is switched ON or OFF by pressing and holding down button for 3 seconds. the
It is also possible to set an Auto-off value in the configuration menu, so that the AHM automatically switches itself off after a preset time, if there is no keyboard activity.
RANGE Button
The range feature allows for the setting of two totally independent setup ranges to be selected, if required. To switch between ranges simply press the range button. If TEDS has been enabled then only 1 range is permissible.
When you enter either the calibration menu or configuration menu, the parameters you will be setting are those for the range you have selected. An annunciator is lit to identify which range has been selected.
The AHM is supplied with engineering unit legends; these can be slid into a window, located on the inside of the front panel. These labels then help to further identify the units being displayed for each range. Please refer to the photo below:-
Legend labels are inserted both sides
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AHM User Manual
HOLD Button
The hold button allows the user to freeze the display when it is pressed. When pressed again the display returns to it’s normal operating mode. When in hold mode the display will flash and the hold annunciator will be lit, to ensure that this feature is not accidentally turned on without the user noticing.
The hold feature can not be used when the AHM is in either peak or trough hold mode.
GROSS/NET Button
The gross/net button, when pressed, toggles between the gross and net display values. This enables the user to zero the display (by putting the AHM into net mode) and displaying the change in display value from that point.
This is useful for certain weighing applications where a tare weight exists, which can be removed by putting the
AHM into net mode.
SHUNT CAL Button
The shunt calibration button, when pressed, puts an internal 100kΩ resistor across the –ve excitation and –ve signal of the sensor, generating a simulated output from the sensor, therefore giving a simulated display value. This can be pressed immediately after the sensor has been calibrated with the AHM and noted down for later reference.
The value noted can be used to get an idea of the calibration accuracy at a later date, or for checking the integrity of the sensor and sensor cabling.
The shunt calibration resistor can be changed to suit specific requirements. It is suggested that a 15ppm ±0.1% tolerance resistor is used.
PEAK Button
When pressed this button puts the AHM into peak mode. This will display the highest display reading and hold it on the display until it is reset or a higher value is reached. To reset the peak display, press the peak and trough buttons simultaneously. In peak mode it is possible to capture peaks at a rate of up to 25Hz. To turn off the peak mode, press the peak button.
TROUGH Button
When pressed this button puts the AHM into trough mode. This will display the lowest display reading and hold it on the display until it is reset or a lower value is reached. To reset the trough display, press the peak and trough buttons simultaneously. In trough mode it is possible to capture troughs at a rate of up to 25Hz. To turn off the trough mode, press the peak button.
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Configuration Menu Parameters
SEt ZEro
Parameter
The
SEt ZEro
parameter is meant to be accessible to the user. It allows the removal of fixed display offset values from the display, so that the GROSS and NET features can operate from a zero point. This may also be considered as a manual tare facility. To zero the display, simply enter the value that you wish to subtract from the display in the
SEt Zero
parameter. i.e. if the display reads 000.103 and you wish it to read 000.000, then enter 000.103 in the
SEt
ZEro
parameter.
Set Zero may also be achieve by pressing Gross/Net and Hold button simultaneously.
Different values can be set for each RANGE.
SEt rAtE
Parameter
The
SEt rAtE
value sets the display update rate. The options available are 25Hz, 10Hz, 3Hz, 1Hz and 0.5Hz.
Different updates rates can be set for each RANGE.
The 25Hz rate only updates at this rate when in the PEAK or TROUGH mode. When in normal display mode it has been limited to a 3Hz update, as the digit fluctuations are impossible to view with the human eye.
The 10Hz, 3Hz, 1Hz and 0.5Hz rates update the display every 100mS, 300mS, 1000mS and 2000mS respectively. The
AHM when it leaves the factory is set at 3Hz.
SEt OVEr
Parameter
The
SEt OVEr
parameter allows the user to set a visual alarm. The value that is entered is the display value that you want the alarm to activate at. When the alarm is activated the word
OVErLOad
appears on the screen. To remove the alarm, the display value must be reduced to a value that is lower than that set in the
SEt OVEr
parameter. This can be very useful as a safety feature, or simply as a quick indication of when a preset level has been reached.
This value entered can be anywhere over the entire display range, so there are no limitations. Different values and settings are available for each RANGE.
SEt OPEr
Parameter
The AHM has a special power saving mode, which can be enabled or disabled within this parameter, pressing when asked whether you wish to select
P SAvE?
will put the AHM into power save mode for the RANGE selected. Pressing will de-activate the power save facility.
When the power save facility is activated, battery life is conserved by pulsing on the excitation voltage to the sensor. As a result the accuracy is reduced, as is the update rate. When in this mode, the quickest update rate is
3Hz and the accuracy of the display is reduced to 1 digit in 10,000. It is important to note these limitations when deciding whether to use the power save facility. However, it is also possible to set one RANGE with power save activated and the other without.
The benefit is that the battery life, based on a 350Ω sensor bridge being connected, increases from 45 hours to 450 hours.
It is also important to remember that when the AHM is re-calibrated with a sensor, the power save facility will be automatically turned off. The power save facility will therefore need to be re-activated after calibration has been completed.
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AUtO OFF
Parameter
The
AUtO OFF
parameter is another power saving feature. It allows for the setting of a time period in minutes, between 05 and 99 (00 de-activates
AUtO OFF
). i.e. if this was set to 25, then if the AHM detects no keyboard activity for a continuous 25 minute period, then the AHM will power down, to conserve power. If keyboard activity is detected at any time during the 25 minute period, then the time period is restarted.
This can be a useful feature in a site environment, should the AHM be left unintentionally powered on.
rS232
Parameter
This parameter allows the user to enable the RS232 output form the AHM, by pressing when prompted by
EnAbLEd?
On the display, pressing will disable the RS232.
The output format is ASCII. The display value is passed to the RS232 port each time the display updates, with a carriage return and line feed at the end of each data string. The string information is as follows:-
Baud Rate
Stop bits
Parity
Data bits
=
=
=
=
9600 baud
1
None
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Calibration Menu Parameters
SEnS 5.0
Parameter
The AHM is factory set to enable calibration with sensors generating an input signal of 5mV/V or less. In the majority of cases it will not be necessary to read higher signal levels. If however, a higher sensitivity sensor is used with the
AHM, it will be necessary to gain access to the internal PCB (you must turn the AHM off) to move link LK1 to JP1
(see picture below) to allow the AHM to accept sensitivities of up to 50mV/V. TEDS should only be used with
5mV/V as 50mV/V is not factory calibrated.
Once this link has been moved, you will need to go back into the CALIBRATION MENU. When re entering the menu, you will notice that the parameter
SEnS 5.0
has changed to SEnS 50.0 to change the sensitivity to 50mV/V press
, the AHM will now check the position of the link and change the sensitivity. It will now be necessary to re-calibrate any sensors that you may previously have calibrated to this instrument.
Sensitivity link should be in this position for use with sensors, with sensitivities
<+/- 5mV/V
Sensitivity link should be in this position for use with sensors, with sensitivities >+/-5mV/V
SEt rES
Parameter
This parameter enables the setting of two features on the AHM. It allows you to set the decimal point position of the display, by pressing the and together, to move the point position (each press moves the decimal point position, one place to the right).
It also allows for the setting of the display resolution or the number of display counts the display changes with an input change. To change the resolution use the and arrows to select a digit you want to change and the
and arrows to increment or decrement the digits. Press to accept the value.
CALibrAt
Parameter (disabled when TEDS is enabled)
This parameter is used to calibrate and scale the AHM with a sensor. There are two basic methods of calibration available. These are
LiVE
and
tAbLE
. There is also a third parameter, which can be used for maintenance and recording purposes. This parameter is
CAL VAL
. The
CAL VAL
value can be viewed after a calibration has been completed and will show the offset and gain figures from any stored calibration. If these figures are noted, they can be used to re-enter at a later date, if calibration data is lost for any reason, or if the calibration data from a sensor needs to be transferred to another AHM.
tedS
Parameter
This parameter automatically calibrates the AHM with the data from the TEDS chip. The two annunciators appear when active connection with a TEDS peripheral has been made. When there is a loss of connection these annunciators flash. When changing a sensor the AHM should be power cycled as this is when the
TEDS data is read. Calibration Procedures are not available when TEDS is enabled.
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TEDS limitations / specifications
ERROR 1 Must be DS2431 or DS2433 Device
ERROR 2 & 3 Must use template 33
Template 33 restrictions
ERROR 6
ERROR 4
ERROR 7
ERROR 5 min physical value = >-9999999.0 max physical value = >9999999.0 value precision case = 1 or 2 min electrical value > -5.0mV/V max electrical value < 5.0 mV/V bridge type = FULL (2)
ERROR 8 excitation min = > 5.0 excitation max = < 5.0
Calibration Procedures
The best method of calibration, if it is possible to do so, is the
LiVE
calibration, as this reads in the sensor signal at two calibration points and scales the AHM automatically. If this is not possible, then the sensitivity figure (in mV/V) from the sensor calibration certificate can be used to scale the AHM, by using the
tAbLE
calibration. This may be the only option available if you are unable to apply a known stimulus to the sensor, which quite often is the case.
LiVE Calibration Procedure
When
CALibrAt
is displayed press
LiVE ?
will now be displayed, press
You will be prompted
uSE SC ?
, this can be selected if you wish to use the shunt calibration figure from a sensor calibration certificate (care should be taken that the shunt calibration resistor used originally with the sensor is the same as is fitted in the AHM). If you wish to use this press otherwise press
You will then be prompted
APPLY LO
. At this point ensure that the low calibration stimulus is applied to the sensor and allow to settle of approx. 3 seconds, then press
You will then be prompted with
dISP LO
. Press to enter the display value required with the low stimulus applied to the sensor. The value can be entered by using the and button to select a digit and the and buttons to change the digit. When the value has been set press
You will then be prompted with
APPLY HI
(unless you chose to
uSE SC ?
, in which case jump to the next stage) At this point ensure that the high calibration stimulus is applied to the sensor and allow to settle of approx. 3 seconds, then press
You will then be prompted with
dISP HI
. Press to enter the display value required with the high stimulus applied to the sensor. The value can be entered by using the and button to select a digit and the and buttons to change the digit. When the value has been set press
You should now see
donE
displayed. This means the calibration was successful, press to the AHM to normal operation mode, with the new calibration data stored. If you see
FaiLEd
, then you will need to repeat the calibration, checking that you have completed the procedure in the correct order, and that the sensor is connected correctly.
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tAbLE Calibration Procedure
When
CALibrAt
is displayed press
LiVE ?
will now be displayed, press
tAbLE ?
will now be displayed, press
You will be prompted with
InPut LO
, press
Now enter the ‘zero’ mV/V output level of the sensor by using the and and buttons to change the digit. When the value has been set press all zeros.
button to select a digit and the
.If you do not know this, simply enter
You will be prompted with
dISP LO
. Press to enter the display value required for the low input figure entered.
button to select a digit and the and buttons to change The value can be entered by using the and the digit. When the value has been set press
You will be prompted with
InPut HI
, press
Now, using the table/value provided by the sensor manufacturer, enter the mV/V output level by using the
button to select a digit and the and buttons to change the digit.
and
When the value has been set press
For example, if you enter a value of 2.5 mV/V for
InPut HI
the display will show ‘2.500000’
You will then be prompted with
dISP HI
. Press entered.
to enter the display value required for the high input figure
The value can be entered by using the and the digit. When the value has been set press
button to select a digit and the and buttons to change
You should now see
donE
displayed. This means the calibration was successful, press to the AHM to normal operation mode, with the new calibration data stored.
If you see
FaiLEd
, then you will need to repeat the calibration, checking that you have completed the procedure in the correct order, and that the sensor is connected correctly.
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Millivolt per Volt Calibration Procedure
This procedure outlines how a millivolt per volt calibration might be undertaken.
1. Ensure that the factory settings for gain and offset are set to 1 and 0, respectively. See millivolt per volt calibration section to do this.
2. Begin by connecting up the model AHM and a high precision Multimeter to the calibration source set at
2.5mV/V with a 350
Ω load.
3. Take readings at 2.5mV/V and 0mV/V on both the model AHM and the high precision Multimeter.
4. Record your excitation reading.
5. To convert Multimeter reading to a millivolt per volt reading, divide the output reading on the meter by the measured value of excitation.
millivolts per volt (mV/V)=
Output Voltage (mV)
_____________
Excitation (V)
[ 1 ]
6. The gain is then calculated by dividing the difference in the span of the Multimeter readings by The model
PSD reading.
7. This value can then be entered into the millivolt per Volt Calibration menu under
5.0 gAIn
then press
to confirm.
8. The offset of the model AHM is derived by subtracting the 0mV/V Multimeter reading from the model PSD reading.
9. Again, enter this under
5.0 OFFS
in the millivolt per Volt Calibration menu then press to confirm.
AHM Reading e.g.
0.000338mV/V @ 0mV/V
2.47993mV/V @ 2.5mV/V
Worked Example
0 mV/V
2.5mV/V
1. Gain = Δ Multimeter reading / Δ AHM reading = (2.49984 - 0.000204423)
(2.47993 - 0.000338)
2. Offset = Multimeter reading – AHM reading = 0.000204423 - 0.000338
= 1.008008mV/V (6dp)
= - 0.000096mV/V (6dp)
Load Cell Central AHM User Manual
Calibration Source
2.5mV/V @ 350
Ω load
Setup Diagram
Multimeter Reading e.g.
12.234mV @ 2.5mV/V
000.001mV @ 0mV/V
Excitation – 4.8939 V @ 2.5mV/V
Excitation – 4.8918 V @ 0mV/V
Using formula above [1]:
0.000204423mV/V @ 0mV/V
2.499846mV/V @ 2.5mV/V
AHM handheld (mV/V) Multimeter (mV/V)
0.000338 0.000204423
2.47993 2.499846
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Specifications
Performance
Control Variables
Mechanical
Environmental
Input Type:
Input Range:
Non Linearity:
Thermal Drift:
Temperature effect on zero (MAX)
Temperature effect on span (MAX)
Offset stability
Gain stability
Excitation Voltage:
Minimum Bridge
Resistance:
Internal Battery:
Battery Life:
Update Rate:
*from original offset at any time @ 2.5mV/V ** 1 st
year
Indication Display Type:
Display Resolution:
Annunciators:
Front Panel User Keys:
Settable Parameters:
Electrical Connection:
Physical Size:
Weight:
Legends:
Operating Temperature:
Environmental Rating:
Enclosure Type:
European EMC Directive
Strain Gauge Full Bridge Sensors
Up ±5mV/V (±50mV/V can be supplied, with factory set option)
± 50ppm of FR
<25 ppm/°C
±7 ppm/°C
±5 ppm/°C
±80 ppm of FR*
±100 ppm of FR**
5Vdc (±4%), 59mA maximum current
85Ω (4off 350Ω sensors in parallel)
2off AA size alkaline, access via sealed rear compartment
45 hours (Typical 450 hours in low power mode), with 350Ω sensor
Up to 40mS (can be set in configuration menu)
7½ digit LCD display, 8.8mm high digits
1 part in 250,000 at 1Hz update rate
1 part in 65,000 at 10Hz update rate
Low Battery warning; peak; trough; hold; net; shunt cal; range
Tactile Keys with recessed rims for:-
ON/OFF Switches AHM power on/off
RANGE Selects between two ranges
HOLD Hold the current display value, press again to release
GROSS/NET Zero’s display (±100% range)
SHUNT CAL Generates simulated input for indicator
PEAK
TROUGH testing
Enables peak hold
Enables valley/trough hold
Tare/Zero value; display resolution/decimal point position; display update rate; low power mode; auto power off;
5 pin Binder socket (mating plug supplied)
See drawing below
250 grams
Insert legends for engineering unit identification (supplied)
-10°C to +50°C
IP65 (when mating plug fitted)
ABS, dark grey (Leather Carry Case Optional)
2004/108/EC
BS EN 61326—1:2006
BS EN 61326-2-3:2006
Mechanical Dimensions
The Case is Registered Design No. 3021311
90 34
kgf kN
Lbs
152
23
Load Cell Central
AHM User Manual
Warranty
The AHM is warranted against defective material and workmanship for a period of (1) one year from the date of dispatch.
If the Load Cell Central product you purchase appears to have a defect in material or workmanship or fails during normal use within the period, please contact your Distributor, who will assist you in resolving the problem. If it is necessary to return the product to Load Cell Central please include a note stating name, company, address, phone number and a detailed description of the problem. Also, please indicate if it is a warranty repair.
The sender is responsible for shipping charges, freight insurance and proper packaging to prevent breakage in transit.
Load Cell Central warranty does not apply to defects resulting from action of the buyer such as mishandling, improper interfacing, operation outside of design limits, improper repair or unauthorised modification. No other warranties are expressed or implied. Load Cell Central specifically disclaims any implied warranties of merchantability or fitness for a specific purpose. The remedies outlined above are the buyer’s only remedies. Load
Cell Central will not be liable for direct, indirect, special, incidental or consequential damages whether based on the contract, tort or other legal theory.
Any corrective maintenance required after the warranty period should be performed by Load Cell Central approved personnel only.
In the interests of continued product development, Load Cell Central reserves the right to alter product specifications without prior notice.
Code No. 517-173 Issue 3.1 22.10.14
Load Cell Central AHM User Manual
24
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