HEAD OFFICE : MITSUBISHI DENKI BLDG MARUNOUTI TOKYO 100-8310 TELEX : J24532 CABLE MELCO TOKYO
HIMEJI WORKS : 840, CHIYODA CHO, HIMEJI, JAPAN
In buffer memory locations (BFMs) marked with an “*” data can be written from the PLC using the TO
instruction.
For buffer memories (BFMs) without “*” mark, data can be read by the PLC using the FROM instruction.
Before reading from the analog special function block, ensure that the appropriate settings have been sent
to the analog special function block. Otherwise, the previous values held in the analog block will be used.
The buffer memory also gives a facility to adjust the offset and gain via software.
Offset (intercept): The analog input value when the digital output becomes 0.
Gain (slope): The analog input value when the digital output becomes +1000.
1) Channel Selection
Channel selection is made by a 4 character HEX number HOOOO in buffer memory BFM #0.
The least significant character controls channel 1 and the 4th character controls channel 4.
Setting of each character is as follows:
O = 0: Preset range (-10V to +10V) O = 2: Preset range (-20mA to +20mA)
O = 1: Preset range (+4mA to +20mA) O = 3: Channel OFF
Example: H3310
CH1 : Preset range (-10V to +10V)
CH2 : Preset range (+4mA to +20mA)
CH3, CH4: Channel OFF
2) Analog to Digital Conversion Speed Change
By writing 0 or 1 to BFM #15 of the FX2N-4AD, the speed at which A/D conversion is performed can be
changed.
However the following points should be noted:
To maintain a high speed conversion rate, use the FROM/TO instructions as seldom as possible.
NOTE:When a conversion speed change is made, BFM #1-#4 are set to their default values
immediately after the change. This is regardless of the values they held originally. Bear this in
mind if a speed change will be made as part of the normal program execution.
3) Adjusting Gain and Offset values
a) When buffer memory BFM #20 is activated by setting it to K1, all settings within the analog special
function block are reset to their default settings. This is a very quick method to erase any
undesired gain and offset adjustments.
b) If (b1, b0) of BFM #21 is set to (1,0), gain and offset adjustments are prohibited to prevent
inadvertent changes by the operator. In order to adjust the gain and offset values, bits (b1, b0)
must be set to (0,1). The default is (0,1).
c) Offset and gain values of BFM #23 and #24 are sent respectively to the offset and gain resisters
in non-volatile memory of the specified input channels. Input channels to be adjusted are
specified by the appropriate G-O (gain-offset) bits of BFM #22.
Example:If bits G1 and O1 are set to 1, input channel 1 will be adjusted when BFM #22 is written
to by a TO instruction.
d) Channels can be adjusted individually or together with the same gain and offset values.
e) Offset and gain values in BFM #23 and #24 are in units of mV or m A. Due to the resolution of the
unit the actual response will be in steps of 5mV or 20 m A.
4) Status Information BFM #29
NOTE: b4 to b7, b9 and b13 to b15 are undefined.
Bit devices of BFM #29 ON OFF
b0 : Error
When any of b1 to b4 is ON.
If any of b2 to b4 is ON, A/D
conversion of all the channels is
stopped.
No error
b1 : Offset/gain error Offset/Gain data in the EEPROM
is corrupted or adjustment error. Offset/Gain data normal
b2 : Power source abnormality 24V DC power supply failure. Power supply normal
b3 : Hardware error A/D converter or other hardware
failure. Hardware Normal
b10 : Digital range error Digital output value is less than
-2048 or more than +2047 Digital output value is normal.
b11 : Averaging error Number of averaging samples is
4097 or more or 0 or less
(default of 8 will be used)
Averaging is normal.
(between 1 and 4096)
b12 : Offset/gain adjust prohibit Prohibit-(b1, b0) of BFM #21 is
set to (1, 0) Permit-(b1, b0) of BFM #21 is
set to (0,1)
5) Identification Code BFM #30
The identification (or ID) code number for a Special Function Block is read using the FROM
instruction.
This number for the FX2N-4AD Special Function Block unit is K2010.
The user’s program in the PLC can use this facility in the program to identify the special function block
before commencing data transfer from and to the special function block.
CAUTION
• Values of BFM #0, #23 and #24 are copied to the EEPROM memory of the FX2N-4AD.
BFM #21 and BFM #22 are only copied when data is written to the gain/offset command
buffer BFM #22. Also, BFM #20 causes the resetting of the EEPROM memory. The
EEPROM has a life of about 10,000 cycles (changes), so do not use programs which
frequently change these BFMs.
• Due to the time needed to write to the EEPROM memory, a delay of 300 ms is required
between instructions that cause a write to the EEPROM.
Therefore, a delay timer should be used before writing to the EEPROM for a second time.
7. DEFINING GAIN AND OFFSET
Offset and gain can be set independently or together. Reasonable offset ranges are -5V to +5V or -20mA
to +20mA, and gain value - offset value = 1V to 15V or 4mA to 32mA. Gain and offset can be adjusted by
software in the main unit (see program example 2)
• Bit device’s b1, b2 of the gain/offset BFM #21 should be set to 0, 1 to allow adjustment.
• Once adjustment is completed these bit devices should be set to 1, 0 to prohibit any further changes.
8. EXAMPLE PROGRAM
8.1 Basic Program
In the following example, channels CH1 and CH2 are used as voltage inputs. The FX2N-4AD block is
connected at the position of special function block No. 0. The number of averaged samples is set at 4 and
data registers D0 and D1 of the main unit receive the averaged digital data.
Gain determines the angle or slope of the
calibration line, identified at a digital value of 1000. Offset is the ’Position’ of the calibrated line,
identified at a digital value of 0.
a) Small gain value: Large steps in digital
readings
b) Zero gain value: default (5V or 20mA)
c) Large gain value:Small steps in digital
readings
d) Negative offset
e) Zero offset: default (0V or 4mA)
f) Positive offset
+1,000
Analog
Digital
Gain value
(a) (b)
(c)
Gain
Analog
Digital
Offset value
(d) (e) (f)
Offset
0
M8002
initial
pulse
FROM K0 K30 D4 K1
CMP K2010 D4 M0
TO K0 K0 H3300 K1
P
M1
TO K0 K1 K4 K2
FROM K0 K29 K4M10 K1
M10 M20 FROM K0 K5 D0 K2
NO
error Digital output
value is normal
The ID code for the special function block at position "0" is
read from BFM #30 of that block and stored at D4 in the main
unit.
This is compared with K2010 to check that the block is a
FX
2N
-4AD, if OK M1 is turned ON. These two program steps
are not strictly needed to perform an analog read. They are
however a useful check and are recommended as good
practice.
The analog input channels (CH1, CH2) are setup by writing
H3300 to the BFM #0 of the FX
2N
-4AD.
The number of averaged samples for CH1 and CH2 is set to 4
by writing 4 to the BFM #1 and #2 respectively.
Do not execute the pulse form of the instruction.
The operational status of the FX
2N
-4AD is read from BFM #29
and output as bit devices of the main unit.
If there are no errors in the operation of the FX
2N
-4AD, then
the averaged data BFM's are read.
In the case of this example BFM #5 and #6 are read into the
main unit and stored in D0 and D1. These devices contain the
averaged data for CH1 and CH2 respectively.
8.2 Using gain and offset in a program
The following is an example of changing the offsetvalue on input channel CH1 to 0V andthe gain value to
2.5V.
The FX2N-4AD block is in the position of block No. 0 (i. e. closest to the main unit).
Example: Adjusting gain/offset by PLC programing
9. DIAGNOSTICS
9.1 Preliminary checks
I. Check whether the input wiring and/or extension cables are properly connected on the FX2N-4AD
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.
IV. Check that there is no power overload on either the 5V or 24V power sources, remember the loading
on a main unit or a powered extension unit varies according to the number of extension blocks or
special function blocks connected.
V. Make sure that the main unit has been switched to RUN.
9.2 Error checking
If the FX2N-4AD special function block does not seem to operate normally, check the following items.
• 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 FX2N-4AD).
Lit :FX2N-4AD is OK, 24V DC power source is OK.
Otherwise :Possible 24VDC power failure, if OK possible FX2N-4AD failure.
• Check the status of the “A/D” LED (top right corner of the FX2N-4AD).
Lit :A/D conversion is proceeding normally.
Otherwise :Check buffer memory #29 (error status). If any bits (b2 and b3) are ON, then this is why
the A/D LED is OFF.
