Yokogawa EJX440A - Manual (Page 34)

<3. Operation>
3-24
IM 01C25T01-01E
3.5.12 CPU Failure Burnout Direction and
Hardware Write Protect
There are two slide switches on the CPU assembly
board. One sets the burnout direction at CPU
failure, and the other sets a write protection function
which disables parameter changes through
the use of a handheld terminal or some other
communication method.
HIGH LOW
CPU assembly
Slide switch
Burnout direction switch
Write protection switch
Write Protection
Switch Position
Burnout Direction
Switch Position
BO H L
WR E D
H L
E D
H L
E D
H L H L
Hardware write protection switch (WR)
Burnout direction switch (BO)
Burnout Direction
Write Protection
YES
(Write disabled)
NO
(Write enabled)
F0339.ai
The parameter of AO alm typ parameter displays
the status of 4-20 mA DC output if a CPU failure
occurs. In case of a failure, communication is
disabled.
Standard specifications
The burnout direction switch is set to HIGH. If a
failure occurs, the transmitter outputs a 110% or
higher signal.
Option code /C1
The burnout direction switch is set to LOW. If a
failure occurs, a –5% or lower output is generated.
F0340.ai
EJX:
Analog output
1 Loop test
2 D/A trim
3 Scaled D/A trim
4 Clear D/A trim
5 AO alm typ High
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1. Device setup
4. Detailed setup
3. Output condition
2. Analog output
5. AO alm typ
Example: Confirming the burnout direction at the CPU
failure.
3.5.13 Software Write Protect
EJX configured data is saved by using a write
protect function. The write protect status is set to
“Yes” when 8 alphanumeric characters are entered
in the New password field and transferred to the
transmitter. When write protect is set to “Yes,” the
transmitter does not accept parameter changes.
When the same eight alphanumeric string entered
in the New password field is also entered in the
Enable wrt 10min field and transferred to the
transmitter, it will be possible to change transmitter
parameters during a 10 minute period.
To change the transmitter from the write protect
“Yes” status back to Write protect “No” status, use
Enable wrt 10min to first release the write protect
function and then enter eight spaces in the New
password field.
The software write protection does not affect the
function of external zero adjustment screw.
To disable the external zero adjustment screw,
select Disabled in the Ext SW field before activating
the software write protection. Refer to subsection
3.5.11.