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6. ALLOCATION OF BUFFER MEMORIES (BFM)
6.1 Buffer memories
BFM
CONTENTS
*#0
Characteristic change
CH1 to CH4 Averaged temperature reading to be
*# 1 - #4
averaged (1 to 256) Default = 8
#5 - #8
CH1 to CH4 Averaged temperature in 0.1°C units
#9 - #12
CH1 to CH4 Present temperature in 0.1°C units
#13 - #16
CH1 to CH4 Averaged temperature in 0.1°F units
#17 - #20
CH1 to CH4 Present temperature in 0.1°F units
#21 - #27
Reserved
*#28
Digital range error latch
#29
Error status
#30
Identification code K2040
#31
Reserved
1) BFM #0 value (K0 or K1) decides the Pt100 characteristic to be used.
K0 : JIS C 1604-1997
K1 : JIS C 1604-1981
2) The number of samples to be averaged are assigned in BFMs #1 to #4. Only the range 1 to 4096 is
valid. Values outside this range are ignored. The default value of 8 is used.
3) A number of recently converted readings are averaged to give a smoother read out. The averaged
data is stored in BFMs #5 to #8 and #13 to #16.
4) BFMs #9 to #12 and #17 to #20 store the current value of the input data. This value is in units of 0.1°C
or 0.1°F, but the resolution is only 0.2°C to 0.3°C or 0.36°F to 0.54°F.
6.2 Status Information
1) Buffer Memory BFM #28: Digital range error latch
BFM #29 b10(digital range error) is used to judge whether the measured temperature is within the
unit's range or not.
BFM #28 latches the error status of each channel.
b15 or b8
b7
b6
b5
b4
High
Low
High
Low
Not used
CH4
CH3
Low : Latches ON when the temperature measurement data drops below the lowest
temperature measurement limit.
High : Turns ON when the temperature measurement data rises above the highest
temperature measurement limit.
When an error occurs the temperature data before the error is latched. If the measured value returns
to within valid limits the temperature data returns to normal operation. (Note: The error remains
latched in (BFM #28))
An error can be cleared by writing K0 to BFM #28 using the TO instruction or turning off the power.
2) Buffer Memory BFM #29: Error status
Bit devices of BFM #29
ON
When either b2 or b3 is ON
b0 : Error
A/D conversion is stopped for
the error channel.
b1 : Reserved
Reserved
b2 : Power source
24V DC power supply failure.
A/D converter or other
b3 : Hardware error
hardware failure.
b4 to b9 : Reserved
Reserved
Digital output/analog input
b10 : Digital range error
value is outside the specified
range.
Selected number of averaged
b11 : Averaging error
results is outside the available
range -see BFM #1 to #4
b12 to b15 : Reserved
Reserved
3) Buffer Memory BFM #30: Identification Code
The identification code or ID number for this Special Block is read from buffer memory BFM #30 using
the FROM instruction. This number for the FX
-4AD-PT unit is K2040.
2N
The PLC can use this facility in its program to identify the special block before commencing data
transfer from and to the special block.
7. SYSTEM BLOCK DIAGRAM
The FX
-4AD-PT communicates
2N
PLC
with the PLC via buffer memories.
Command
information
BFMs (buffer memories) #21 to #27
write and
and #31 are reserved.
data status
All BFM data can be read by the
read
PLC using the FROM instruction.
P L C c a n r e a d / w r it e t h e B F M s
(marked with "*" ), using FROM /TO
instructions.
24V DC
Power Source
8. EXAMPLE PROGRAM
In the program shown below, the FX
is the third closest block to the PLC). The averaging amount is four. The averaged values in degrees C of
input channels CH1 to CH4 are stored respectively in data registers D0 to D3.
M8002
FNC78
FROM
Initiali-
zation
FNC10
Pulse
CMP
M8000
FNC78
FROM
RUN
monitor
M10
b3
b2
b1
b0
High
Low
High
Low
CH2
CH1
M1
FNC79
TO
or
M8000
FNC78
OFF
FROM
No error
Reserved
Power supply normal
Hardware Normal
Reserved
Digital output value is normal.
Averaging is normal.
(between 1 to 4096)
Reserved
POWER
LED
5V Power
Gain and offset
Supply
values are
Buffer
stored in the
TO
Memory
EEPROM
RAM
Analog Input
Photocoupler
CPU
FROM
Converted
data
A/D
System
converter
ROM
Control
signals
Multiplexer
A/D
±15V
LED
DC/DC
Cyclic switching
5V
5V
converter
24V
LED
FX
-4AD-PT Analog Block
2N
-4AD-PT block occupies the position of special block number 2 (that
2N
Block No.2 BFM #30 → (D10)
K2
K30
D10
K1
Identification code
When (K2040) = (D10), M1 = ON
K2040 D10
M0
i.e. When identification code is K2040, M1 = ON
This initial step checks that the special function block placed at position 2 is
actually an FX
-4AD-PT, i.e. its unit identification number is 2040 (BFM #30).
2N
This step is optional, but it provides a software check that the system has been
configured correctly.
Block No.2 BFM #29 → (K4M10)
K2
K29 K4M10 K1
Transfer the error status to (M25 to M10).
When error is found, M10 = ON.
Y010
Represents b0 BFM #29
This step provides optional monitoring of the FX
-4AD-PT Error Buffer Memory
2N
(#29). If there is an Error on the FX
-4AD-PT, bit b0 of BFM #29 will be set on.
2N
This can be read by this program step, and output as a bit device in the PLC (Y010 in
this example). Additional Error devices can be output in a similar manner, i.e. b10 BFM
#29. (see below)
M8000
FNC78
K2
K29
K4M10
K1
FROM
M10
Represents b0 BFM #29
Y010
M20
Y011
Represents b10 BFM #29
(K4) → (BFM #1 to #4)
K2
K1
K4
K4
Number of samples is changed to four on CH1 to CH4.
(BFM #5 to #8) → (D0 to D3)
K2
K5
D0
K4
Transfer the averaged temperature value in °C to the
data registers.
This step is the actual reading of the FX
-4AD-PT input channels. It is essentially
2N
the only program step which is needed. The "TO" instruction in this example, sets
the input channels, CH1 to CH4, to take the average reading of four samples.
The "FROM" instruction reads the average temperatures (BFM #5 to #8) for input
channels CH1 to CH4 of the FX
-4AD-PT. If direct temperature readings are
2N
required BFM #9 to #12 should be read instead, ex.
FNC78
K2
K9
D0
K4
FROM
special
FX
-4AD-PT
result
No. of
2N
block No.2
BFM number
destination
words read
9. DIAGNOSTICS
9.1 Preliminary checks
I.
Check whether the input/output wiring and/or extension cables are properly connected on the FX
4AD-PT analog special function block.
II. Check that the PLC system configuration limits have not been exceeded, i.e. the number of special
function blocks, and the total system I/O are within the specified range.
III. Ensure that the correct operating range has been selected for the application.
CH1
IV. Check that there is no power overload on either the 5V or 24V power sources, remember the loading
CH2
on main unit or a powered extension unit varies according to the number of extension blocks or
CH3
special function blocks connected.
CH4
V. Make sure that the main unit has been switched to RUN.
9.2 Error checking
If the FX
-4AD-PT special function block does not seem to operate normally, check the following items.
2N
•
Check the status of the POWER LED.
Lit
:The extension cable is properly connected.
Otherwise :Check the connection of the extension cable.
•
Check the external wiring.
•
Check the status of the "24V" LED (top right corner of the FX
Lit
:FX
-4AD-PT is ON, 24V DC power source is ON.
2N
Otherwise :Possible 24V DC power failure, if ON possible FX
•
Check the status of the "A/D" LED (top right corner of the FX
Lit
:A/D conversion is proceeding normally.
Otherwise :Check buffer memory #29 (error status). If any bits (b0, b2, b3) are ON, then this is why
the A/D LED is OFF.
10.EMC CONSIDERATIONS
Electromagnetic compatibility or EMC must be considered before using the FX
Mitsubishi recommend that the PT 100 sensors used, should be fitted with a form of seild or screening as
protection against EMC noise.
If some form of cable protection is used, the "Shield" must be terminated at the
as shown in section 4.1.
Because of the delicate nature of all analog signals, failure to take good EMC precautions could lead to
EMC noise induced errors; up to ±10% of actual values. This is an absolute worst case figure, users who
do take good precautions can expect operation within normal tolerances.
EMC considerations should include selection of good quality cables, good routing of those cables away
from potential noise sources.
Additionally it is recommended that signal averaging is used as this will reduce the effects of random noise
"spikes".
This manual confers no industrial property rights or any rights of any other kind, nor does it confer any
patent licenses. Mitsubishi Electric Corporation cannot be held responsible for any problems involving
industrial property rights which may occur as a result of using the contents noted in this manual.
Manual number : JY992D65601
Manual revision : E
Date
HEAD OFFICE : TOKYO BUILDING, 2-7-3 MARUNOUCHI, CHIYODA-KU, TOKYO 100-8310, JAPAN
HIMEJI WORKS : 840, CHIYODA CHO, HIMEJI, JAPAN
-
2N
-4AD-PT).
2N
-4AD-PT failure.
2N
-4AD-PT).
2N
-4AD-PT.
2N
FG
terminals
: September 2007
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