Isolated Universal inputs, OR
Non-Isolated RTD inputs
›Modbus option
For easy integration with
SCADAs and PLCs
›4 Digital inputs›Auto-detecting RS232/
RS485 serial port
›Easy USB programming
defineinstruments.com/
workbench
1
Zen RTU
Remote Terminal Unit
General Description
The Zen RTU/U is a Remote Terminal Unit
made for harsh industrial environments. Each
channel is isolated and EMC hardened. The
universal input is one of the most exible on
the market, making it a breeze to interface to
a wide range of sensors.
The Zen RTU/R provides a lower cost, non-
isolated temperature (RTD) only version, suitable for more benign applications like cool
store monitoring.
Both units have 16 input channels, enabling
you to collate a large number of signals, and
simply and eciently route them to your PLC
or SCADA system.
Our free WorkBench conguration soware
is designed to assist and even teach you how
to congure the unit, and provides a range of
easy-to-use presets and exible controls. The
intuitive help panel follows you during setup
and updates automatically with relevant tips,
wiring diagrams, and application examples.
Equipment protected throughout by
DOUBLE INSULATION or REINFORCED
INSULATION.
ORDER CODES
ZEN–RTU/––
3
Zen RTUSupply Voltage
InputU
R
Supply VoltageHV
MV
Port 1 Comm
EMOD
16 x Isolated Universal Inputs
16 x Non-isolated RTD Inputs
85–265V AC / 95–370V DC
24–48V AC / 17–72V DC
No Port 1 Comm
Ethernet Modbus
SAFETY NOTICES
For your safety and the prevention of damage to the Zen unit and other equipment
connected to it, please read complete instructions prior to installation and op-
eration of the Zen and carefully observe all safety regulations and instructions.
Consult this manual carefully in all cases where hazard symbols are marked on
your Zen unit.
Use of this instrument in a manner not specied by the manufacturer may compromise the protection provided by the instrument. This instrument should not be used
to directly drive valves, motors, or other actuators, unless equipped with appropriate safeguards.
It is the responsibility of the user to identify potential hazards that may arise in
the event of a fault to unit, and implement safeguards for the prevention of harm
to persons or equipment. The safety of any system incorporating this unit is the
responsibility of the assembler of the system.
The Zen should be installed in a location that
does not exceed the maximum operating
temperature, and at a safe distance from
other devices that generate excessive heat.
The installation environment should provide
good air circulation to the unit.
The plastic casing and product label may be
cleaned, if required, using a so, damp cloth
and neutral soap product. Caution should
be exercised when cleaning the unit to
avoid water dripping inside, as this will
damage the internal circuits.
2.3 - Installation instructions
The Zen RTU is rated IP20, and should be mounted in an enclosure to protect the unit from
weather conditions and dust.
A - Installation in Enclosure (Fig 1)
Prepare an Enclosure (not supplied) as illustrated by mounting a DIN 35 rail, cable
glands, and any other required components.
If using a metal enclosure, the enclosure
must be earthed.
B - DIN Rail Mounting (Fig 2)
To clip the unit onto the DIN rail:
(1) Hook the lower part of the unit onto the
rail, and then
(2) Press down towards the rail until the red
hooks click into place
Leave at least 2" (5cm) clear above and below the unit, to allow room for airow and
wiring.
Fig 1
7
C - Wiring
Refer to Sections 5–6 in this manual.
D - Removal from DIN Rail (Fig 3)
To remove the unit from the DIN rail:
(1) Power down the unit
(2) Unplug the 'Input 4' and 'Port 1' connectors from the top of the Zen (the DIN clips
are behind these terminals)
(3) Gently pull the unit away from the rail
while levering one of the clips upward with
a screwdriver
(4) When one side is loosened, hold it slightly away from the rail to prevent the clip from
engaging again (pictured in Fig 3).
Meanwhile, lever the second clip upward as
you did with the rst.
The Zen has been designed to cope with
large EMC disturbances. This has been
achieved by continual testing and improvement of ltering and layout techniques over
many years.
The Zen meets CE noise requirements, and
even surpasses them in many tests. (For
full details and test results, see Appendix
A.) However in some applications with less
than optimum installations and large power
switching, the EMC performance of the Zen
can be further improved, by:
A Installing the unit in an earthed Metal
Enclosure. This is particularly useful
if the control box is mounted close to
large power switching devices like contactors. Every switching cycle there is a
possibility of generating a large amount
of near eld radiated noise. The Metal Enclosure, acting as a faraday cage,
will shunt this radiation to ground and
away from the Zen.
B Increasing the physical distance from
the power devices. For example, increasing the control box distance from
6" to 12" from the noise source will reduce the noise seen by the control box
by a factor of 4. (Probably the cheapest
and best results in this situation could
be obtained by adding RC snubbers to
the contactors or power switches.)
C Using shielded cable on sensitive input
and control signal lines. Good results
can be obtained by grounding the
shields to the metal enclosure close to
the entry point. All cables act as aerials and pick up unwanted R.F. radiated
signals and noise; the earthed shield
acts as a faraday cage around the cables, shunting the unwanted energy to
ground.
Shields can also help with capacitively
coupled noise typically found in circumstances when signal cable is laid on top
of noisy switching power cables. Of
course in this case you are better o to
keep separate signal and power lines.
D Laying cable on earthed cable trays
can also help reduce noise seen by the
Zen. This is particularly useful if there
are long cable runs, or the unit is close
to radiating sources such as two way
radios.
E The relay outputs of the Zen have built
in MOV's to help reduce EMI when
switching inductive loads. EMI can further be reduced at the load by adding
snubbers for AC signals or a yback diode for DC coils.
Dene WorkBench oers a comprehensive and yet simple-to-use setup tool for your Zen RTU.
You must install WorkBench before connecting the Zen RTU to your computer. If you have
already connected using the Bridge Key, please disconnect before continuing.
A Download the latest version of WorkBench from
deneinstruments.com/workbench
B Extract the install le from the zip folder. Right-click on the zip folder and choose
'Extract All', (or extract the le using another extraction utility of your choice).
INSTALLING DEFINE WORKBENCH
C Double-click on the extracted .msi
install le. This will launch the
WorkBench installer.
Depending on your security settings,
a 'Security Warning' dialog may
appear. If you see the security
message, click 'Run'.
To program your Zen RTU, connect
one end of the Interface Cable to the
programming port on the le side of
the Zen (see Fig 4), and the other end
to your Bridge Key.
Then plug the Bridge Key into your
computer's USB port (see Fig 5).
Supply Power
Supply power to the Zen RTU, referring
to 5.1 for wiring.
Bridge Key
Interface Cable
Zen RTU
Connect to your Zen in Dene WorkBench
Launch Dene WorkBench (see Section 3 for installation instructions), and select the 'Prog
Port' tab. If your Zen is powered up and connected via the Bridge Key, then the COM Port will
be detected automatically. Click 'Connect'.
Main Navigation, including channel sub-navigation. See 4.3 for more information.
Control Area
Main control area for conguring your
system. Any changes made in this area will
bring up the Apply Button (see below)
Connection Panel
Disconnect button
Connection status
Apply Button
Appears if you have made any changes in the
Control Area. WorkBench will not allow you to
browse to a new tab in the Main Navigation with
unapplied changes to your conguration.
Wiring diagrams, explanations
and helpful tips will automatically appear in this panel as
you congure the Zen.
4.3 - Main navigation
13
Overview
View basic device information including Serial Number and rmware version. Password
Protect your device, export a conguration
certicate and save/upload a conguration
le.
Ports
This tab is only visible if you are connected to
your Zen via the USB Programming Port. It
enables you to congure a range of settings
for Port 1 and Port 2 (baud rate, parity, Tx
delay etc.).
Once your ports are set up, you will be able
to congure to your Zen in WorkBench via
Port 1 or Port 2 instead of the USB programming port - perfect for adjusting settings
once your unit is installed.
Inputs
Set up and scale the 16 input channels.
Includes integrated wiring diagrams and
examples.
Digital Inputs
Set up the four digital inputs and view their
live status.
Totalizers
Congure up to 10 totalizers using either an
input channel or a digital input as the source.
Totalizers are only available for the Zen
RTU/U.
Plugins
Plugins are small programs which are loaded
into the Zen to expand its functionality or
simplify its use. Plugins are optional and in
many cases they may not be needed. Note
that only one plugin can be installed on your
Zen at a time.
The Zen RTU has 10 LED indicators on the top label (or 8, for units with no comms option installed in Port 1). These LED's provide information about the unit's status, as explained below:
ON = Digital Input Active
OFF = Digital Input Inactive
ON = Power is supplied to the unit
FLASHING = Normal operation
Indicates activity on the
5.3 - Digital inputs
The Zen RTU has four Digital Inputs (A–D), each with LED
indication on top of the unit. The digital inputs can be
congured and scaled using Dene WorkBench from the
"Digital Inputs" tab, as per the list below:
›Status (active/inactive - can be read by a SCADA
system as a general digital input)
›Counter (up to 10KHz, or 100Hz Debounced)›Frequency (up to 10KHz)›Flow count (up to 10KHz)›Flow rate (up to 10KHz)›RPM (up to 10KHz)
NOTE
For the Zen RTU/U, the universal analog inputs can also be wired as digital pulse
inputs (see 6.5).
Risk of electric shock. Dangerous and lethal voltages may be present on the input termi-
nals. Please take appropriate precautions to ensure safety.
CAUTION
Risk of danger. The sensor input can potentially oat to dangerous and unexpected volt-
ages depending on what external circuit it is connected to. Appropriate considerations
must be given to the potential of the sensor input with respect to earth common.
6.1 - Current input
Range 0–20mA, 4–20mA
Input impedance 45Ω
Maximum over-range protected by PTC
to 24V DC
Linearity & repeatability 0.1% FSO max
Channel separation 0.001% max
Ambient dri 0.003%/°C FSO typical
RF immunity 1% eect FSO typical
Zen RTU/U
Accuracy 0.1% FSO max
0/4–20mA DC is the most commonly used analog signal in industry, and is universally accepted.
As a current loop, it is unaected by voltage drops in cables, and can be transmitted over long
distances without signal degradation. Current input is accepted by the Zen RTU/U only.
If you are connecting other instruments in a loop
with a Zen mA input, a fail-safe has been added to
prevent the external loop from being interrupted in
the event of a power loss to the Zen.
To activate the fail-safe for an input channel, turn
on the micro switch above the input terminal. You
will need to remove the input connector to see the
switch, and use a small screwdriver to turn it on.
NOTE
The Fail-Safe Micro Switch is only compatible with mA inputs on the Zen RTU/U.
For the accurate operation of this instrument, it is critical that the micro switch be
set to the OFF position for all other input types.
Connection example for 2, 3 & 4 wire mA output transmitters
+24V Supply
Fail-safe Micro Switch
2-Wire
Transmitter
Output +
Output −
Output +
Output −
Power
Supply
3-Wire
Transmitter
4-Wire
Transmitter
Note 1 All analog inputs are isolated to
other channels and all other voltages.
They also have built in over voltage protection to 24V, protecting the unit if the
24V supply is inadvertently connected to
the unit when congured for mA input.
Note 2 All cables must be screened, with
Note 3 Do not run input cables in close
vicinity to noisy power supplies, contactors or motor cables. The best practice is
to run input cables on a separate earthed
cable tray. This will minimise RFI eects,
of which magnitude cannot be easily
predicted.
The Zen RTU/U accepts both voltage and millivolt inputs. Along with the standard 0–10V DC
range, a variety of other ranges are provided to suit a various applications. These can all be
selected using the WorkBench soware and easily scaled into engineering units.
The ±200mV DC and -200mV to 1V DC ranges are ideal for low signal applications, such as
measuring large DC currents using external current shunts, or interfacing to sensors with low
voltage output. A 0–18V general purpose voltage range is also provided.
Connection Example for Millivolt & Voltage Inputs for 2, 3 & 4 Wire
Transmitters
+24V Supply
2-Wire
Transmitter
B+
B–
Input
Channel
Output +
Output −
Output +
Output −
Power
Supply
3-Wire
Transmitter
4-Wire
Transmitter
Note 1 Each voltage input must not see
more than 18V peak between the negative and the input, otherwise permanent
damage may occur.
Note 2 All cables must be screened, with
screen earthed at one end only.
B+
Input
Channel
B–
B+
Input
Channel
B–
Note 3 Do not run input cables in close
vicinity to noisy power supplies, contactors or motor cables. The best practice is
to run input cables on a separate earthed
cable tray. This will minimise RFI eects,
of which magnitude cannot be easily
predicted.
RTD input is accepted by both the Zen RTU/R and the Zen RTU/U.
The RTD is highly stable and accurate. Oen referred to as Pt100 and
Pt1000, the Pt represents platinum, and 100/1000 is the resistance in
ohms at 0°C.
Supported RTD types/ranges
Pt100/Pt1000 (0.02°F/0.01°C res)-328 to 572°F (-200 to 300°C)
Pt100/Pt1000 (0.1°F/0.1°C res)-328 to 1472°F (-200 to 800°C)
Connection Example for 3-Wire RTD
Inputs
A
Input
B
Channel
B
A
Input
B
Channel
B
A
B
B
Input
Channel
Sensor fail upscale
Accuracy (RTU/R)
-328–572°F (-200–300°C) = ±0.2°C
-328–1472°F (-200–800°C) = ±0.3°C
Accuracy (RTU/U)
-328–572°F (-200–300°C) = ±0.1°C
-328–1472°F (-200–800°C) = ±0.3°C
Ambient dri 0.003°C/°C typical
Note 1 Inputs are isolated for the Zen RTU/
U, and non-isolated for the Zen RTU/R.
Note 2 All RTD cables must be screened,
with screen earthed at one end only. All
three wires must be the same resistance
(i.e. the same type and size).
Note 3 To minimise lead resistance errors,
3-wire RTD’s should be used. Oset errors
for 2-wire RTD’s may be compensated for
in the soware.
Note 4 Do not run input cables in close
vicinity to noisy power supplies, contactors or motor cables. The best practice is
to run input cables on a separate earthed
cable tray. This will minimise RFI eects,
of which magnitude cannot be easily
predicted.
Thermocouple types B, E, J, K, N, R, S or
T type (see table below for ranges)
Cold junction compensation 14 to 140°F
(–10 to 60°C)
CJC dri <0.02°C/°C typical for all inputs
The thermocouple
is one of the most
common temperature sensors used in
industry. It relies on
the Seebeck coecient
between dissimilar
metals. The thermocouple type is selected
with reference to the
application temperature range and environment, with J and K
type being the most common.
Connection Example for
Thermocouple Inputs
B+
B–
B+
B–
B+
B–
Note 1 All thermocouple inputs are isolated from each other. There is no need to
buy expensive isolated thermocouples.
Thermocouple
Input
Channel
Input
Channel
Input
Channel
Zen RTU/U
Sensor open Upscale
TC lead resistance 100Ω max
Input impedance >500KΩ
Accuracy 0.1% of FSO ±1°C typical
Supported thermocouple types/ranges
B32 to 3272°F(0 to 1800°C)
E-328 to 1292°F(-200 to 700°C)
J-328 to 1832°F(-200 to 1000°C)
K-328 to 2300°F(-200 to 1260°C)
N-328 to 2372°F(-200 to 1300°C)
R32 to 3092°F(0 to 1700°C)
S32 to 3092°F(0 to 1700°C)
T-328 to 752°F(-200 to 400°C)
Note 2 For accurate thermocouple mea-
surements (especially at low temperatures) the top cover must always be tted.
Avoid dras and temperature dierences
across terminals. Once installation is complete, close the cabinet door and allow
the cabinet to reach equilibrium. This may
take several hours. Place all thermocouple
probes into a calibrated thermal bath at
temperature of interest. Any osets can
be zeroed out in the soware.
Note 3 All thermocouples are referenced
to a combination of four CJC temperature sensors on the main Zen board. This
minimizes errors caused by the mounting
orientation of the Zen unit, and temperature dierences in enclosures. However,
for high accuracy applications it is still
Note 4 All cables must be screened, with
screen earthed at one end only.
Note 5 When thermocouple inputs are selected, an upscale resistor is automatically
connected to the T/C + input, resulting in
an overow condition for open or broken
sensors.
6.5 - Digital pulse
Frequency range 0–2500.0Hz
Fast counter range 0–2500.0Hz
Sensors Open collector (NPN, PNP), TTL
or Clean Contact
The Zen RTU/U's 16 universal input terminals
accept digital inputs from NPN, PNP or TTL
sensors as well as Clean Contacts. Pulses up
to 2.5kHz can be counted (except for the
debounced counter, which has a range of
0–50Hz).
A variety of operating modes are soware
programmable to suit your application.
Note 4 Do not run input cables in close
vicinity to noisy power supplies, contactors or motor cables. The best practice is
to run input cables on a separate earthed
cable tray. This will minimise RFI eects,
of which magnitude cannot be easily
predicted.
Zen RTU/U
Frequency resolution 0.1Hz
Debounce counter range 0–50Hz max
Counter register output 32 bit
Accuracy ±0.5%
Soware programmable modes include:
›General counter›General debounced counter (ideal for
mechanical relay contacts which are
subject to bouncing)
each other. Inputs from various sources
can be connected without fear of crating unwanted and troublesome ground
loops.
Note 2 Soware selectable functions
include: frequency to 2kHz, debounced
counter for contact closures to 100Hz
maximum, fast counter to 20KHz.
Note 3 All cables must be screened, with
screen earthed at one end only.
Note 4 Do not run input cables in close
vicinity to noisy power supplies, contactors or motor cables. The best practice is
to run input cables on a separate earthed
cable tray. This will minimise RFI eects,
of which magnitude cannot be easily
predicted.
Zen RTU/U
Field prog span 0.1–100%
Linearity and repeatability
<±0.05% FSO typical
Response time 100msec
Temperature dri <50ppm/°C
A 3 wire potentiometer is typically used to measure position. A low or
high potentiometer range can be programmed to your unit using the
WorkBench soware.
These ranges must be calibrated using the two point calibration method.
Below is a list of the commonly used Zen RTU registers. For a full register list, please see the
Zen Registers document, available at: deneinstruments.com/zen-registers
Your Zen RTU has been fully calibrated at the factory, and can be recalibrated in soware using Dene WorkBench (see Section 4). Scaling to convert the input signal to a desired display
value is also done using WorkBench
If your Zen unit appears to be behaving incorrectly or inaccurately, refer to troubleshooting
before attempting to calibrate it. When recalibration is required (generally every 2 years), it
should only be performed by qualied technicians using appropriate equipment.
Calibration does not change any user programmed parameters. However, it may aect the
accuracy of the input signal values previously stored.
8.2 - Troubleshooting
IssueResolution
Input signal is not reading
correctly on Zen RTU/U
Auto-detecting RS Port is
not working
Beat light stays ON for
more than 1 minute
Cannot power up unitCheck the power supply connections and supply range. (The
Ethernet device does not
appear on the network
when trying to connect in
WorkBench
Check positioning of fail-safe micro switch
The fail-safe micro switch should be switched o for all input
types except mA. See 6.1 to conrm.
Ensure that any terminal connections marked 'NC' are le
open - otherwise the Zen will not be able to auto-detect
your serial type.
This indicates an error. Please return the Zen RTU to the
manufacturer for analysis and repair.
polarity on the power input is irrelevant.)
Repower the device aer you plug in the ethernet cable to
ensure that it appears on the network.
For further assistance, please contact technical support using the contact details listed at the
end of this document.