Woodward MRU3-1 User manual

MRU3-1 – AC voltage relay
(September 2008)
Manual MRU3-1 (Revision New)

Woodward Manual MRU3-1 GB
2 TD_MRU3-1_09.08_GB_Rev.New
Woodward Governor Company reserves the right to update any portion of this publication at any time. Information
provided by Woodward Governor Company is believed to be correct and reliable. However, no responsibility is as-
sumed by Woodward Governor Company unless otherwise expressly undertaken.
© Woodward 1994-2008

Manual MRU3-1 GB Woodward
TD_MRU3-1_09.08_GB_Rev.New 3
Contents
1.Introduction and application ....................................................................... 5
2.Features and characteristics....................................................................... 6
3.Design ........................................................................................................... 7
3.1Connections ...................................................................................................................... 7
3.1.1Analog input circuits ...................................................................................................... 8
3.1.2Blocking input................................................................................................................ 8
3.1.3Reset input .................................................................................................................... 8
3.1.4Output relays................................................................................................................. 8
3.1.5Fault recorder................................................................................................................ 8
3.1.6Parameter settings ...................................................................................................... 10
3.2LEDs ............................................................................................................................... 11
3.3Front plate ....................................................................................................................... 11
4.Working principle ....................................................................................... 12
4.1Analog circuits................................................................................................................. 12
4.2Digital circuits .................................................................................................................. 12
4.3Voltage supervision......................................................................................................... 12
4.3.1Selection of star or delta ............................................................................................. 13
4.4Blocking function ............................................................................................................. 14
5.Operations and settings ............................................................................ 15
5.1Display ............................................................................................................................ 15
5.2Setting procedure............................................................................................................ 17
5.3Systemparameter............................................................................................................ 17
5.3.1Display of residual voltage UEas primary quantity (Uprim/Usec) .................................... 17
5.3.2D/Y – Switch over........................................................................................................ 17
5.3.3Setting of nominal frequency....................................................................................... 18
5.3.4Display of the activation storage ................................................................................. 19
5.3.5Parameter switch/external triggering for the fault recorder.......................................... 19
5.4Protection parameters..................................................................................................... 20
5.4.11-phase or 3-phase U</U>-tripping............................................................................. 20
5.4.2Parameter setting of over- and undervoltage supervision........................................... 20
5.4.3Adjustment of the slave address ................................................................................. 20
5.4.4Setting of Baud-rate (applies for Modbus-Protocol only)............................................. 20
5.4.5Setting of parity (applies for Modbus-Protocol only).................................................... 20
5.5Parameter for the fault recorder ...................................................................................... 21
5.5.1Adjustment of the fault recorder .................................................................................. 21
5.5.2Number of the fault recordings .................................................................................... 21
5.5.3Adjustment of trigger occurrences............................................................................... 21
5.5.4Pre-trigger time (Tpre)................................................................................................... 21
5.6Date and time.................................................................................................................. 22
5.6.1Adjustment of the clock ............................................................................................... 22
5.7Indication of measuring values........................................................................................ 22
5.7.1Measuring indication ................................................................................................... 22
5.7.2Unit of the measuring values displayed....................................................................... 22
5.7.3Indication of fault memory data ................................................................................... 22
5.8Fault memory .................................................................................................................. 23
5.9Additional functions ......................................................................................................... 24
5.9.1Setting procedure for blocking the protection functions............................................... 24
5.9.2Reset........................................................................................................................... 25
5.9.3Erasure of fault storage............................................................................................... 25
6.Relay testing and commissioning ............................................................ 26
6.1Power-On ........................................................................................................................ 26
6.2Testing the output relays................................................................................................. 26
6.3Checking the set values .................................................................................................. 27
6.4Secondary injection test .................................................................................................. 28
6.4.1Test equipment ........................................................................................................... 28
6.4.2Example of the test circuit ........................................................................................... 28

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6.4.3Checking the input circuits and measuring functions................................................... 29
6.4.4Checking the operating and resetting values of the over/under-voltage functions ...... 29
6.4.5Checking the relay operating time of the over/under voltage functions ....................... 29
6.4.6Checking the external blocking and reset functions .................................................... 30
6.5Primary test ..................................................................................................................... 30
6.6Maintenance.................................................................................................................... 30
7.Technical Data ............................................................................................ 31
7.1Measuring input circuits................................................................................................... 31
7.2Common data.................................................................................................................. 31
7.3Setting ranges and steps................................................................................................. 32
7.3.1Interface parameter ..................................................................................................... 32
7.3.2Parameter for the fault recorder .................................................................................. 32
7.4Output relays ................................................................................................................... 33
8.Order form................................................................................................... 34

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TD_MRU3-1_09.08_GB_Rev.New 5
1. Introduction and application
The voltage supervision relay MRU3-1 protects electrical power generators, consumers or operat-
ing components generally against over- or under-voltages.
Among other applications the relay can be used for detection of over- or undervoltages in power
genrating plants and energy supply systems
•to protect generators against critical overvoltages in case of defective voltage regulators
•as undervoltage protection for motors
•as generator stator earth fault protection
•as over- and undervoltage protection with evaluating the symmetrical components
(MRU1-2, detailed information on this type can be found in the relevant technical
description)
There is also a similar protection relay IRU1 avail-able in a more simpler design, i.e. with less func-
tion, without display and without serial interface.

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2. Features and characteristics
•Microprocessor technology with watchdog,
•digital filtering of the measured values by using discrete Fourier analysis to suppress
higher harmonics and d.c. components induced by faults or system operations,
•two parameter sets,
•voltage supervision each with two step under-/ and overvoltage detection,
•Completely independent time settings for voltage supervision
•display of all measuring values and setting parameters for normal operation as well as trip
ping via a alphanumerical display and LEDs,
•display of measuring values as primary quantities
•1-phase or 3-phase tripping criterion for the U</U> step,
•Storage and display of tripping values in a fault memory (voltage-failure safe),
•recording of up to eight fault occurences with time stamp
•for blocking the individual functions by the external blocking input, parameters can be set
according to requirement,
•suppression of indication after an activation (LED flash),
•free assignment for output relays,
•display of date and time,
•in compliance with VDE 0435, part 303 and IEC 255,
•serial data exchange via RS485 interface possible; alternatively with SEG RS485 Pro-
Open Data Protocol or Modbus Protocol.
Important:
For additional common data of all MR-relays please refer to technical description "MR - Digital Mul-
tifunctional Relays".

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3. Design
3.1 Connections
Figure 3.1: Connection of the MRU3-1 to phase-to-phase voltage
Note: Connection of phase-to-neutral voltage is possible too.
Figure 3.2: Voltage transformer in V-connection

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3.1.1 Analog input circuits
The external wiring of the measuring circuits are shown in the connection diagram. The analog in-
put voltages are galvanic ally decoupled by the input transformers of the device, then filtered and
finally fed to the analog digital converter. The measuring circuits can be connected in star or delta
connection.
3.1.2 Blocking input
When required to inhibit functions of the relay, the auxiliary voltage has to be switched to D8/E8.
Please refer to chapter 4.4.
3.1.3 Reset input
Please refer to chapter 5.9.2.
3.1.4 Output relays
The MRU3-1 is equipped with 5 output relays.
•Relay 1; C1, D1, E1 and C2, D2, E2
•Relay 2; C3, D3, E3 and C4, D4, E4
•Relay 3; C5, D5, E5
•Relay 4; C6, D6, E6
•Relay 5; Signal self-supervision (internal failure of the unit ) C7, D7, E7
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay.
3.1.5 Fault recorder
The MRU3-1 has a fault value recorder which re-cords the measured analog values as instantane-
ous values. The instantaneous values
UL1; UL2; UL3 for star connection
U12; U23; U21 for delta connection
are scanned at a raster of 1.25 ms (at 50 Hz) and 1.041 ms (at 60 Hz) and saved in a cyclic buffer.
It is possible to store 1 - 8 fault occurences with a total recording time of 16 s (with 50 Hz) and
13.33 s (with 60 Hz) per channel.
Storage division
Independent of the recording time, the entire storage capacity can be divided into several cases of
disturbance with a shorter recording time each. In addition, the deletion behavior of the fault re-
corder can be influenced.
No writing over
If 2, 4 or 8 recordings are chosen, the complete memory is divided into the relevant number of
partial segments. If this max. number of fault event has been exceeded, the fault recorder block
any further recordings in order to prevent that the stored data are written over. After the data have
been read and deleted, the recorder to ready again for further action.
Writing over
If 1, 3 or 7 recordings are chosen, the relevant number of partial segments is reserved in the com-
plete memory. If the memory is full, a new re-cording will always write over the oldest one.

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The memory part of the fault recorder is designed as circulating storage. In this example 7 fault re-
cords can be stored (written over).
Memory space 6 to 4 is occupied.
Memory space 5 is currently being written in
Figure3.3: Division of the memory into 8 segments, for example
Since memory spaces 6, 7 and 8 are occupied, this example shows that the memory has been as-
signed more than eight recordings. This means that No. 6 is the oldest fault recording and No. 4
the most recent one.
Figure 3.4: Basic set-up of the fault recorder
Each memory segment has a specified storage time which permits setting of a time prior to the
trigger event.

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3.1.6 Parameter settings
System parameters
Uprim/Usek Primary/secondary measured value
display of the voltage transformers
Δ/ Y Selection of switching groups fN Rated frequency
P2|FR Parameter switch/ext. triggering for the fault recorder
LED-Flash Suppression of LED flashing after activation
Protection parameters
1/3 1-phase U</U> or 3-phase U</U> tripping
U< Tripping value for undervoltage low set element
tU< Tripping delay time for undervoltage low set element
U<< Tripping value for undervoltage high setelement
tU<< Tripping delay time for undervoltage high set element
U> Tripping value for overvoltage low set element
tU> Tripping delay time for overvoltage low set element
U>> Tripping value for overvoltage high set element
tU>> Tripping delay time for overvoltage high set element
Parameters for the fault recorder
FR Number of disturbance events
FR Trigger events
FR Pre-trigger time Tvor
Date and time
Year Y = 00
Month M = 04
Day D = 18
Hour h = 07
Minute m = 59
Second s = 23
Additional functions
Blocking function
Relay configuration
Fault memory

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3.2 LEDs
All LEDs (except LED RS, FR and P2) are two-colored. The LEDs on the left side, next to the al-
phanumerical display light up green during measuring and red after tripping.
The LEDs below the push button <SELECT/RESET> are lit green during setting and inquiry proce-
dure of the setting values which are printed on the left side next to the LEDs. The LEDs will light up
red after parameterizing of the setting values next to their right side.
The LED marked with letters RS lights up during setting of the slave address of the device for serial
data communication.
The LED marked with the letters FR is alight while the fault recorder is being adjusted.
If the LED is displayed, date and time are shown.
3.3 Front plate
Figure3.5: Front plate MRU3-1

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4. Working principle
4.1 Analog circuits
The input voltages are galvanically insulated by the input transformers. The noise signals caused
by inductive and capacitive coupling are suppressed by an analog R-C filter circuit.
The analog voltage signals are fed to the A/D-converter of the microprocessor and transformed to
digital signals through Sample- and Hold- circuits. The analog signals are sampled with a sampling
frequency of 16 x fN, namely, a sampling rate of 1.25 ms for every measuring quantity, at 50 Hz.
4.2 Digital circuits
The essential part of the MRU3-1 relay is a powerful microcontroller. All of the operations, from the
analog digital conversion to the relay trip decision, are carried out by the microcontroller digitally.
The relay program is located in an EPROM (Electrically-Programmable-Read-Only-Memory). With
this program the CPU of the microcontroller calculates the three phase voltage in order to detect a
possible fault situation in the protected object.
For the calculation of the voltage value an efficient digital filter based on the Fourier Transformation
(DFFT - Discrete Fast Fourier Transformation) is applied to suppress high frequency harmonics
and d.c. components caused by fault-induced transients or other system disturbances. The micro-
processor continuously compares the measured values with the preset thresholds stored in the pa-
rameter memory (EEPROM). If a fault occures an alarm is given and after the set tripping delay
has elapsed, the corresponding trip relay is activated.
The relay setting values for all parameters are stored in a parameter memory (EEPROM - Electri-
cally Erasable Programmable Read Only Memory), so that the actual relay settings cannot be lost,
even if the power supply is interrupted.
The microprocessor is supervised by a built-in "watchdog" timer. In case of a failure the watchdog
timer resets the microprocessor and gives an alarm signal via the output relay "self supervision".
4.3 Voltage supervision
The voltage relay MRU3-1 protects electrical generation systems, consumers and appliances in
general against over- and/or under voltage. The relay is equipped with an independent, 2-step
over- (U>, U>>) and under voltage supervision (U<, U<<) with separately adjustable tripping values
and delay times. Voltage measuring is 3-phase. In this process there is a continuous comparison of
the line conductor voltages in case of a delta connection and of the phase voltages in case of a
star connection with the preset limit values.
With the MRU3-1 the highest voltage is always evaluated for overvoltage supervision and the low-
est voltage for under voltage supervision.
A distinction is made between 1-phase and 3-phase tripping. (1/3 – Parameter)
With 1-phase tripping the voltages are evaluated as follows:
U</U<</U</U>>: Activation or tripping takes place if at least one phase has fallen short of the trip-
ping value.
With 3-phase tripping the voltages are evaluated as follows:
U<: Activation or tripping takes place if all three phases have fallen short of the tripping value.
U<<: Activation or tripping takes place if one phase has fallen short of the tripping value.
U>: Activation or tripping takes place if all three phases have exceeded the tripping value.
U>> Activation or tripping takes place if one phase has exceeded the tripping value.

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4.3.1 Selection of star or delta
All six connections of the input voltage transformers are led to screw terminals. The nominal vol-
tage of the device is equal to the nominal voltage of the input transformers. Dependent on the ap-
plication the input transformers can be connected in either delta or star. The connection for the
phase-to-phase voltage is the delta connection. In star connection the measuring voltage is re-
duced by 1/√3 . During parameter setting the connection configuration either Y or delta has to be
adjusted.
Figure4.1: Input v.t.s in delta connection (D)
Figure4.2: Input v.t.s in star connection (Y)

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4.4 Blocking function
No. Dynamic Behaviour U</<< U>/>>
1 voltage to external blocking
input is applied
free programmable free programmable
2 blocking input is
released
released
instantaneously
released
instantaneously
3 supply voltage is
switched on
blocked for
200 ms
blocked for 200 ms
4 3ph measuring volt. is sud-
denly applied
released released
5 one or several measuring
voltages are switched off sud-
denly (phase failure)
released released
Figure 4.3: Dynamic behavior of MRU3-1 functions
Blocking function set in compliance with requirements:
The MRU3-1 has an external blocking input. By applying the auxiliary voltage to input D8/E8, the
requested protection functions of the relay are blocked (refer to chapter 5.9.1)

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5. Operations and settings
5.1 Display
Function Display shows Pressed pushbutton Corre-
sponding
LED
Normal operation SEG
Measured operating values Actual measured
values
<SELECT/RESET> one
time for each value
L1, L2, L3,
Transformer ratio of the CT’s (SEK) 1.01 –
6500=prim
<SELECT/RESET><+><-> L1, L2, L3
Setting values:
star/delta connection
Y/DELT <SELECT/RESET><+><->
Δ/Y
Parameter switch/ext. trigger-
ing for the fault recorder
SET1, SET2, B_S2,
R_S2, R_S2, B_FR,
R_FR, S2_FR
<SELECT/RESET><+><-> P2
Switch-over LED flash
No LED flash
FLSH
NOFL
<SELECT/RESET>
<+><->
undervoltage (low set)
tripping delay of low set ele-
ment
setting value in volt
setting value in sec-
onds
<SELECT/RESET><+><->
one time for each value
U<
tU<
undervoltage (high set)
tripping delay of high set ele-
ment
setting value in volt
setting value in sec-
onds
<SELECT/RESET><+><->
one time for each value
U<<
tU<<
overvoltage (low set)
tripping delay of low set ele-
ment
setting value in volt
setting value in sec-
onds
<SELECT/RESET><+><->
one time for each value
U>
tU>
overvoltage (high set)
tripping delay of high set ele-
ment
setting value in volt
setting value in sec-
onds
<SELECT/RESET><+><->
one time for each value
U>>
tU>>
rated frequency setting value in Hz <SELECT/RESET><+><-> fN
U</U> 1-phase/3-phase U<>1/U<>3 <SELECT/RESET><+><-> 1/3
Blocking function EXIT <+> until max. setting value
<-> until min. setting value
LED of
blocked
parameter
Slave address of serial inter-
face
1 - 32 <SELECT/RESET><+><-> RS
Baud-Rate 1) 1200-9600 <SELECT/RESET> <+><-> RS
Parity-Check 1) even odd no <SELECT/RESET> <+><-> RS
Recorded fault data:
star--connection: U1, U2, U3
tripping values in
Volt
<SELECT/RESET><+><->
one time for each phase
L1, L2, L3,
U<, U<<,
U>, U>>
delta-connection: U12, U23,
U31
tripping values in
Volt
<SELECT/RESET><+><->
one time for each phase
L1, L2, L3,
U<, U<<,
U>, U>>
Save parameter? SAV? <ENTER>
Save parameter! SAV! <ENTER> for about 3 s
Delete fault memory wait <-> <SELECT/RESET>
Enquiry fault memory FLT1; FLT2..... <-><+> L1, L2, L3
U<, U<<,
U>, U>>
Trigger signal for the fault re-
corder
TEST, P_UP, A_PI,
TRIP
<SELECT/RESET> <+><-> FR

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Function Display shows Pressed pushbutton Corre-
sponding
LED
Number of fault occurences S = 2, S = 4, S = 8 <SELECT/RESET> <+><-> FR
Display of date and time Y = 99, M = 10,
D = 1,
h = 12, m = 2, s = 12
<SELECT/RESET> <+><-> 
Software version First part (e.g. D02-)
Sec. part (e.g. 6.01)
<TRIP>
one time for each part
Manual trip TRI? <TRIP>
three times
Inquire password PSW? <SELECT/RESET>/
<+>/<->/<ENTER>
Relay tripped TRIP <TRIP> or fault tripping
Secret password input XXXX <SELECT/RESET>/
<+>/<->/<ENTER>
System reset ⏐SEG <SELECT/RESET>
for about 3 s
1) only Modbus
Table 5.1: Possible indication messages on the display

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5.2 Setting procedure
For parameter setting a password has to be entered first (please refer to 4.4 of description
"MR-Digital Multifunctional Relays").
5.3 Systemparameter
5.3.1 Display of residual voltage UEas primary quantity (Uprim/Usec)
The residual voltage can be shown as primary measuring value. For this parameter the transforma-
tion ratio of the VT has to be set accordingly. If the parameter is set to "sec", the measuring value
is shown as rated secondary voltage.
Example:
The voltage transformer is used for 10 kV/100 V. The transformation ratio is 100 and this value has
to be set accordingly. If still the rated secondary voltage should be shown, the parameter is to be
set to 1.
5.3.2 D/Y – Switch over
Depending on the mains voltage conditions, the input voltage transformers can be operated in delta
or Y connection. Changeovers are effected via the <+> and the <-> keys and stored with
<ENTER>.

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5.3.3 Setting of nominal frequency
For proper functioning it is necessary to first adjust the rated frequency (50 oder 60 Hz).
It can be selected between „f = 50 Hz“, „f = 60 Hz“ or „v = 50 Hz“, “v = 60 Hz”.
The difference lies in the method of voltage measuring.
With the setting "v = 50 Hz or v = 60 Hz“ voltage measuring is independent of the existing fre-
quency. This means, the voltage value can be correctly measured between 40 Hz and 70 Hz with-
out adverse effects from the frequency.
With the setting "f“ = 50/60 Hz the measured volt-age value is influenced by the frequency. (see
Table 5.2)
This difference in settings is required for the fault recorder. If the fault recorder is to be used, the
setting must be f = 50 Hz or f = 60 Hz.
At 50 Hz or 60 Hz the fault recorder determines 16 measured values per period. With the setting "v
= 50 Hz or v = 60 Hz" 16 measured values of the presently measured frequency would always be
determined. The disturbance recorder would not indicate any frequency changes and thus render
incorrect measuring results.
Setting v = 50 f = 50 v = 60 f = 60
Rated frequency* 50 Hz 50 Hz 60 Hz 60 Hz
Influence on voltage
measurement
none 0.5..1%/Hz
(see table 5.1)
none 0.5..1%/Hz
(see table 5.1)
Fault recorder Recording
distorted**
Recording
correct***
Recording
distorted**
Recording
correct***
Influence on all other
functions
none none none none
Table 5.2: Deviation of measured value at 50 Hz or 60 Hz
* Setting is important for correct recording of fault recorder
** Sample rate is variably adjusted to the momentarily measured frequency. 16 samples are always measured in one period.
*** Sample rate setting is fixed to 50 Hz or 60 Hz. 16 samples per 20 ms or 16.67 ms are always measured.

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5.3.4 Display of the activation storage
If after an activation the existing current drops again below the pickup value, e.g. U<, without a trip
has been initiated, LED U< signals that an activation has occured by flashing fast. The LED keeps
flashing until it is reset again (push button <RESET>). Flashing can be suppressed when the pa-
rameter is set to NOFL.
5.3.5 Parameter switch/external triggering for the fault recorder
By means of the parameter-change-over switches it is possible to activate two different parameter
sets. Switching over of the parameter sets can either be done by means of software or via the ex-
ternal inputs RESET or blocking input. Alternatively, the external inputs can be used for Reset or
blocking of the triggering of the fault recorder.
Software-parameter Blocking input used as RESET input used as
Software-
parameter
Blocking input used as RESET input used as
SET1 Blocking input RESET input
SET2 Blocking input RESET input
B_S2 Parameter switch RESET input
R_S2 Blocking input Parameter switch
B_FR External triggering of the fault recorder Reset input
R_FR Blocking input External triggering of the fault recorder
S2_FR Parameter switch External triggering of the fault recorder
With the settings SET1 or SET2 the parameter set is activated by software. Terminals C8/D8 and
D8/E8 are then available as external reset input or blocking input.
With the setting B_S2 the blocking input (D8, E8) is used as parameter-set change-over switch.
With the setting R_S2 the reset input (D8, E8) is used as parameter-set change-over switch. With
the setting B_FR the fault recorder is activated immediately by using the blocking input. On the
front plate the LED FR will then light up for the duration of the recording. With the setting R_FR the
fault recorder is activated via the reset input.
With the setting S2_FR parameter set 2 can be activated via the blocking input and/or the fault re-
corder via the reset input.
The relevant function is then activated by applying the auxiliary voltage to one of the external in-
puts.
Important note:
When functioning as parameter change over facility, the external input RESET is not available for
resetting. When using the external input BLOCKING the protection functions must be deactivated
by software blocking separately (refer to chapter 5.9.1).

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5.4 Protection parameters
5.4.1 1-phase or 3-phase U</U>-tripping
Switching-over of the parameter permits selection between 1-phase and 3-phase tripping of the
U</U> steps.
Keys <+> or <-> are used to change the value and <ENTER> to store it.
Note
When the MRU3-1 is to be used for measuring the residual voltage in systems with isolated or
compensated neutral or as generator earth fault protection, the measuring voltage has to be ap-
plied to terminals
A3-A4. Undervoltage functions U< and U<< have to be set to "EXIT" and overvoltage functions U>
and U>> have to be adjusted to the required pickup values.
The frequency must be set to 50 or 60 Hz. The parameter 1-phase or 3-phase tripping must be set
to U<>1 (1-phase tripping).
5.4.2 Parameter setting of over- and undervoltage supervision
The setting procedure is guided by two colored LEDs. During setting of the voltage thresholds the
LEDs U<, U<<, U> and U>> are lit green. During setting of the trip delays tU>, tU>>, tU< and tU<< the
according LEDs light up red.
Thresholds of the voltage supervision
During setting of the threshold U>, U>>, U< and U<< the displays shows the voltages directly in
volt. The thresholds can be changed by the <+> <-> push buttons and stored with <ENTER>.
The under voltage supervision (U< and U<<) as well as the overvoltage supervision (U> and U>>)
can be de-activated by setting the threshold to "EXIT".
Tripping delay of voltage supervision
During setting of the tripping delays tU<, tU<<, tU> and tU>> the display shows the value directly in
seconds. The tripping delay is changed via the push button <+> and <-> in the range of 0,04 s to
50 s and can be stored with the push button <ENTER>.
When setting the tripping delay to "EXIT" the value is infinite meaning only warning, no tripping.
5.4.3 Adjustment of the slave address
By pressing push buttons <+> and <-> the slave address can be set in the range of 1 - 32. During
this adjustment the LED RS lights up.
5.4.4 Setting of Baud-rate (applies for Modbus-Protocol only)
Different transmission rates (Baud rate) can be set for data transmission via Modbus Protocol.
The rate can be changed by push buttons <+> and
<-> and saved by pressing <ENTER>.
5.4.5 Setting of parity (applies for Modbus-Protocol only)
The following three parity settings are possible :
•"even" = even parity
•"odd" = odd parity
•"no" = no parity check
The setting can be changed by push buttons <+> and <-> and saved by pressing <ENTER>.