Westermo RM-505U-K User Manual
505U-K Radio Telemetry Module
ELPRO Technologies Pty Ltd, 9/12 Billabong Street, Stafford Q 4053, Australia.
Tel: +61 7 33528600 Fax: +61 7 33528677 Email: sales@elprotech.com
User Manual
for 505K-2-E, -B, refer to separate User Manual
Web: www.elprotech.com
505K Radio Telemetry Module User Manual
Thank you for your selection of the 505U-K module for your
telemetry needs. We trust it will give you many years of valuable
service.
ATTENTION!
Incorrect termination of supply wires may
cause internal damage and will void warranty.
To ensure your 505U-K enjoys a long life,
double check ALL your connections with
the user’s manual
before turning the power on.
ELPRO Technologies Pty Ltd 2008 Page 2
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WARNING
1. For 505K modules, a radio licence is not required in most countries, provided the
module is installed using the antenna and equipment configuration permitted. Check
with your local 505U distributor for further information on regulations.
2. For 505U modules, operation is authorised by the radio frequency regulatory authority
in your country on a non-protection basis. Although all care is taken in the design of
these units, there is no responsibility taken for sources of external interference. Some
delay in the operation of outputs may occur during periods of interference. Systems
should be designed to be tolerant of these delays.
3. To avoid the risk of electrocution, the antenna, antenna cable, serial cables and all
terminals of the 505U module should be electrically protected. To provide maximum
surge and lightning protection, the module should be connected to a suitable earth and
the antenna, antenna cable, serial cables and the module should be installed as
recommended in the Installation Guide.
4. The 505U module is not suitable for use in explosive environments without additional
protection.
ELPRO Technologies Pty Ltd 2008 Page 3
505K Radio Telemetry Module User Manual
505U-K Radio Telemetry Module
USER MANUAL
1 OVERVIEW ------------------------------------------------------------------------------------------6
1.1 I
1.2 P
1.3 R
1.4 C
NPUT SIGNALS
OWER SUPPLY
ADIO TRANSMITTER
ONFIGURATION
................................................................................................. 6
............................................................................................... 7
............................................................................................... 7
........................................................................................ 7
2 OPERATION ---------------------------------------------------------------------------------------- 8
2.1 N
2.2 W
2.3 H
2.4 I
ORMAL OPERATION
HAT INFORMATION IS TRANSMITTED OVER THE RADIO
OW OFTEN IS THE INPUT INFORMATION SENT BY RADIO
NPUTS
............................................................................................................. 9
......................................................................................... 8
? ...................................... 8
? ..................................... 8
2.4.1 Digital Inputs............................................................................................. 9
2.4.2 Pulse Inputs ............................................................................................. 9
2.4.3 Shaft Encoder Inputs.............................................................................. 11
2.4.4 Pulse Rates ............................................................................................ 11
2.4.5 Analogue Inputs ..................................................................................... 11
2.4.6 Setpoint Status ....................................................................................... 13
2.4.7 Supply Voltage ....................................................................................... 13
2.4.8 Low Supply Voltage Alarm (Supply LowVolts) ....................................... 13
2.4.9 Supply Failure ........................................................................................ 14
2.4.10 Communications Failure......................................................................... 14
2.5 H
OW TO DESIGN A REMOTE MONITORING SYSTEM
............................................ 14
2.5.1 Achieving reliable radio transmission ..................................................... 14
2.5.2 How far will the radio transmit? .............................................................. 15
2.6 C
ALCULATING POWER CONSUMPTION
.............................................................. 16
3 HARDWARE INSTALLATION---------------------------------------------------------------- 19
3.1 H
3.2 A
OW TO MOUNT THE
NTENNA INSTALLATION
505K .............................................................................. 19
.................................................................................. 20
3.2.1 Dipole antenna. ...................................................................................... 21
3.2.2 Yagi antenna. ......................................................................................... 21
3.2.3 Collinear antenna. .................................................................................. 22
3.3 C
ONNECTION PLUG
......................................................................................... 22
3.3.1 PL1-K Plug Lead .................................................................................... 24
P
OWER SUPPLY
......................................................................................................... 25
3.4.1 Battery Pack BU-5-2............................................................................... 25
3.4.2 External Power ....................................................................................... 26
3.5 I
NPUT SIGNAL CONNECTIONS
........................................................................... 26
3.5.1 Digital/Pulse Inputs................................................................................. 26
3.5.2 Shaft Encoder Connections.................................................................... 27
3.5.3 Analogue input ....................................................................................... 27
3.5.4 RS232 serial port.................................................................................... 28
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4 CONFIGURATION------------------------------------------------------------------------------- 30
4.1 I/O M
4.2 U
4.3 D
4.4 A
4.5 A
4.6 S
4.7 P
APPING
PDATE TRANSMISSION TIMES
IGITAL INPUTS
NALOGUE INPUT
NALOGUE SETPOINTS
UPPLY VOLTAGE
ULSE INPUTS
.................................................................................................. 31
.............................................................................................. 32
............................................................................................ 33
.................................................................................... 34
........................................................................................... 35
................................................................................................ 36
......................................................................... 32
4.7.1 Manually Setting Counter Values ........................................................... 38
4.7.2 Shaft Encoder Inputs.............................................................................. 39
4.7.3 Pulse Rates ............................................................................................ 39
4.8 N
4.9 P
4.10 L
4.11 P
UMBER OF TRANSMISSIONS
ROGRAMMING CONFIGURATION FROM TO MODULE
OADING CONFIGURATION FROM A MODULE
RINT OPTIONS
.............................................................................................. 41
........................................................................... 40
...................................................... 40
........................................... 40
5 DIAGNOSTICS AND TESTING -------------------------------------------------------------- 42
5.1 S
5.2 LED I
5.3 D
YSTEM PROBLEMS
NDICATORS
IAGNOSTIC FEATURES
........................................................................................ 42
............................................................................................ 42
................................................................................... 42
5.3.1 Read Inputs ............................................................................................ 43
5.3.2 Setting Counter Values .......................................................................... 43
5.3.3 Calibrating Analog Input ......................................................................... 43
5.3.4 Tone Reversals ...................................................................................... 45
5.3.5 Firmware Version ................................................................................... 45
6 SPECIFICATIONS ------------------------------------------------------------------------------- 46
7 WARRANTY--------------------------------------------------------------------------------------- 48
ELPRO Technologies Pty Ltd 2008 Page 5
505K Radio Telemetry Module User Manual
1 OVERVIEW
Note: Please refer to the separate 505U-2 User Manual for the 505U-2-E and 505U-2-B
products. The 505U-K product will be referred to as the “505K” for the rest of this manual
to clearly delineate it from the other 505U products.
The 505K radio telemetry module is an economical solution for the remote monitoring of
process signals. The 505K can connect to digital, pulse or analogue signals from process
transducers, and transmit these signal values by radio.
Although the 505K is intended to be simple in its application, it also provides many
sophisticated features. This manual should be read carefully to ensure that the modules are
configured and installed to give reliable performance. The 505K has been designed to use a
European licence-free radio band at 869MHz. The 505K uses the 869MHz 105U module as a
receiver, or repeater. If you have not used 105U modules before, please read the 105U User
Manual prior to reading this manual.
The 505K module is a monitoring only unit - that is, it will only accept input signals and
does not provide output signals. The 505K has an internal radio transmitter; it does not have
a receiver to receive messages from another module.
The 505K transmits the value of an input signal whenever the signal changes, and also after a
pre-configured time. Each transmission message includes error-checking to confirm the
validity of the message. At each transmission, the 505K may be configured to repeat the
transmission several times to ensure that the transmission is received correctly. This is
important if the radio path is marginal (that is, the radio signal is not strong) or if there is a lot
of radio traffic on the radio channel which may corrupt the 505K message. The 505K
transmits the input message to a 105U module, which sets an output signal to be the same
value as the 505K input, or the 105U passes the input message to another device (PC or PLC)
via its serial port.
For more information on the 105U module, please refer to the 105U User Manual.
The 505K has a heavy duty painted aluminium enclosure, weather-proof to IP66. Signal and
power connections to the unit are made via a weatherproof connector at the bottom of the
module. Antenna connection is made using a SMA coaxial connector at the top of the
module.
1.1 Input Signals
The 505K module provides two digital/pulse inputs and one analogue input for connecting to
process transducers.
Digital Signals
Examples: motor fault, tank overflow, intruder alarm
Pulse signals - use the same input as the digital input
Examples: electricity metering, fluid flow, raingauge, level from a shaft encoder
Analogue continuously variable signals (0-20mA, 4-20mA, 0-10mA, 0-10V)
Examples: measured tank level, measured process temperature
Some internal signals may also be transmitted to outputs in the network:
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• Setpoint Status (digital signal set or reset depending upon the value of the analogue signal
compared to a high and a low setpoint value configured in the 505K)
• Supply Low Voltage (digital signal set when supply voltage is low).
• Supply Voltage (analogue value)
• Pulse Rate (analogue value proportional to rate of pulse input - available for both pulse
inputs)
1.2 Power Supply
The power consumption of the 505K is very small as it conserves power by reverting to
“sleep” mode between transmissions. The 505K can be powered from a 6 - 30 VDC supply.
An optional 9VDC battery pack, the BU-5-2 is available to power the 505K. The battery
supply uses six AA alkaline batteries. More than one BU-5-2 battery pack can be connected
together to supply a 505K. Other battery supplies can also be used to power the 505K,
including a solar panel supply.
The 505K unit provides an internal alarm on low supply voltage - this alarm may be
transmitted by radio for warning purposes. The user can configure the voltage at which the
low voltage alarm activates.
The 505K generates a 24VDC, 50mA supply for powering the analogue loop. This supply is
designed to power an analogue loop only and should not be used for any other purpose.
1.3 Radio Transmitter
The 505K has an internal radio transmitter that operates on a unlicensed radio channel at
869.4 – 869.65 MHz. A radio licence is not required for the 505K in many European
countries and has an operating range of up to five kilometres.
It is suitable for use in utility industries such as electricity, water and gas, as well as a cost
effective solution for short range applications in factories and industrial plants.
To extend radio range, 105U modules can be used as repeaters. Up to five repeaters can be
configured for each input-to-output link. The configuration is done at the 505K module
where the input signal is - no additional configuration is required at the 105U modules. The
transmitted radio message will include the address of repeater modules - modules with these
addresses will re-transmit the messages.
1.4 Configuration
Each module must be configured before it can be used. Configuration is performed using a
PC (or a laptop computer) connected to the module via the internal RS232 port on the 505K.
505K configuration software is required and is provided with each order.
Configuring a module requires the entering of “input mappings” and setting operating
parameters for each input. An “input mapping” links an input signal to an output channel at a
remote module (or a “destination address”). An input mapping is entered for each input
signal (external and internal) which is used. Mappings may be inverted such that the output is
the reverse value of the input.
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505K Radio Telemetry Module User Manual
2 OPERATION
2.1 Normal Operation
Once configured using the 505K configuration software, the 505K module will normally be in
“sleep” mode to conserve power. During sleep mode, the microprocessor controller powers
down, and the analogue loop supply is turned off. The microprocessor will automatically
“wake up” and revert to full operation if a digital/pulse input changes (on to off, or off to on),
or every 0.5 seconds to check if a timed update transmission is due to be sent.
Normal operation of the 505K is indicated by a brief flicker of the OK LED light on the front
panel approximately every 10 seconds.
2.2 What information is transmitted over the radio?
The 505K modules transmit the value of the input signal in a data frame. The data frame
includes a system address, and the "address" of the transmitting (or “source”) 505K module
and the receiving (or “destination”) 105U module, so that each transmitted message is acted
on only by the correct receiving unit. The system address is a common address used by all
modules in the same system. This allows multiple systems to operate within the same radio
range without "cross-talk" between systems.
The user configures these addresses as part of the module configuration. Each transmitted
message also includes error checking to ensure that no corruption of the data frame has
occurred due to noise or interference. If repeater modules are being used, then the addresses
of these intermediate modules are also included in the data frame.
The user can configure the 505K to transmit each message from one to five times to ensure
that at least one of the messages is received correctly. Each repeat transmission will occur at
random intervals between ??one and four seconds.
2.3 How often is the input information sent by radio?
• Change messages. The 505K transmits the value of an input signal whenever the signal
changes.
• Update messages. The input value is also transmitted if the signal has not changed within
a pre-configured update time (configurable 10 seconds to 7 days).
• Paralysis. When a 505K transmits a message for a particular input, the 505K will not
transmit another message for this input within a configured time period. This time is
called the paralysis time, and may be used to prevent a lot of messages being transmitted
if an input changes frequently. The paralysis time may be set from zero to 127.5 seconds
for each input. For example, assume the paralysis time on an input is 30 seconds. If the
input changes, then the 505K will transmit a message, however it will not transmit another
message for this input during the next 30 seconds, regardless of changes to the input
signal. Note that paralysis time does not stop re-transmissions of each message - if the
505K is configured to transmit each message three times, then paralysis will not stop this.
Depending on the type of input signal (digital, pulse or analogue), the 505K must determine
what type of signal change is required to send a transmission:
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2.4 Inputs
2.4.1 Digital Inputs
A digital input can be an external digital input or an internal status input (setpoint status or
low voltage alarm). The 505K will accept digital inputs as voltage-free contacts, NPN
devices (such as proximity switches) or TTL signals. For TTL signals, a 0-1.5V signal will
be measured as on/active/1, and a 3.5-13V signal will be measured as off/inactive/0.
The 505K will transmit the value of the digital input whenever it changes from off to on or
from on to off. A paralysis time may be configured to prevent another transmission within
this time. The 505K will also transmit an update message if a message has not been
transmitted for that input within an “update time”.
There are two update times for each digital input - one for when the input is on, and one for
when the input is off. Each update time may be configured between 10 seconds and 5 days.
For example, a digital input may be configured to update every 1 day when the input is off,
but update every 10 minutes when the input is on. If an update time of zero (or less than 10
seconds) is selected, then no update messages will be sent.
Overview:
• Input value transmitted on input change
• Update message if the input value has not been transmitted within the configured update
time for that input (10 seconds - 7 days)
• Separate update times for on and off status for digital inputs
• After each transmission, further transmission for that input is disabled for the paralysis
time (0 – 127.5 sec).
The time response of the two digital inputs is different. DI1 has a fast response, sensing a
change within 10msec. This means that the overall “input-to-output’ response is approx 50
msec. DI2 is checked every 500msec - the maximum response time of this input could be
550 msec.
2.4.2 Pulse Inputs
Pulse inputs use the same input connection as the digital inputs. The total number of digital
and pulse inputs available is two.
Each pulse input is counted as two 16 bit registers. The first register is the pulse count, and
the second register is the count of “overflows” of the first register - these two registers
provide a 32 bit count of the pulse input. Each register can be transmitted individually. A
“sensitivity” value is configured for each pulse input (0 - 32 000). Whenever the pulse count
has increased by this value since the last transmission, the 505K will transmit the new pulse
count. In addition, an update transmission of the pulse count will be transmitted if the pulse
count has not been transmitted for the update time. If an update time of zero is selected, then
no update messages will be sent.
The maximum pulse input is:
300Hz for contact or NPN inputs (1 msec minimum on-time and off-time), or
10KHz (30 µsec minimum on-time and off-time) for TTL inputs. Up to 50KHz can be
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505K Radio Telemetry Module User Manual
achieved on PI2 provided the divider is set such that the scaled count rate is less than
10KHz (see below).
There is no minimum pulse rate. For PI2, there is a configurable scaling divider (integer 1 –
255). This allows the pulse count to be scaled. If a divider of X is configured, then the pulse
count will increase by 1 for each X input pulses. There is a separate divider for each pulse
input. The divider parameter could be used for the following reasons:
If the pulse count is to be transmitted to a pulse output on a 105U, then the maximum
pulse rate is 100Hz. If the input rate is more than 100Hz, then it can be reduced with the
divider. For example, if the maximum input rate is 300Hz, then the use of a 10 divider
will bring the effective rate down to 30Hz - each output pulse will then represent 10
input pulses.
The divider can be used to scale the pulse count to engineering units. For example, if the
input pulse rate is 7 pulses per m3 of gas, then a divider of 7 will result in a pulse count
corresponding to the number of m3 . Note that the divider must be an integer.
The divider could be used to slow down the pulse rate. If the input pulse rate is 5KHz,
then the base 16 bit counter will overflow in approx 13 seconds. If the overflow counter
is not used, then this may be too fast to be processed by HMI software. If a divider of
100 is used, then the counter will take over 20 minutes to overflow.
There is no divider for PI1.
If the pulse count is transmitted to a pulse output on a 105U module, the 105U will compare
the input count to its own output count (the count of output pulses), and will then output
pulses until the two counts are the same. If the pulse counts are transmitted to a 105U-C or
105U-G interface module, then the 105U-C will store the pulse count value in an internal
register.
For pulse rates higher than 10 Hz, the “Fast Pulsed Inputs” option should be selected. This
increases power consumption of the module significantly and is not suitable for a battery
power supply.
Overview:
• Pulse inputs are counted as 2 x 16 bit registers.
• Pulse count is transmitted when the count has increased by the sensitivity amount since
the last transmission.
• Update message if the input value has not been transmitted within the update time (10
seconds - 7 days).
• After each transmission, another transmission for that input is disabled for the paralysis
time (0 – 127.5 sec).
• PI2 can be scaled by a configurable divider.
The diagnostics functions of the 505K allow the user to manually set the counter values to any
value (refer section 5 of this manual). On initial start-up of the modules, the counter values
will be zeroed. If the module loses power, the 505K will save the counter values to nonvolatile memeory before shutting down - these values will be restored when power is
restored.
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2.4.3 Shaft Encoder Inputs
The two pulse inputs may be configured to control one up/down count value, for use with
quadrature and incremental shaft encoders. A shaft encoder is a transducer that measures
level or displacement, and has two pulse signals to indicate change of level and direction of
change. Both pulse inputs are read at the same time. The divider parameter on PI2 must be
set to 1 for this application.
If an incremental encoder is used, then the calculated count value is stored in PI1. If a
quadrature encoder is used, then the calculated count value is stored in PI2.
The counter value (or “level position”) can be manually set using the 905K diagnostics
features (refer section 5 of this manual). Initially the counter will need to be “zeroed” when
the shaft encoder is in the “zero level” position.
2.4.4 Pulse Rates
The rate of each pulse count is calculated and can be transmitted as internal analogue inputs.
The rate is calculated on the increase of the base counter, not the rate of the input pulses. The
maximum count rate which can be calculated is 1000Hz. For PI1, this is the maximum pulse
rate that can be calculated. For PI2, a divider can be used for pulse rates more than 1KHz.
The pulse rate values can be scaled - that is, the user can configure what pulse rate (0.1 –
1000Hz) corresponds to maximum analogue value (20mA). Each pulse rate can be scaled
individually. Note that this is separate to the divider on PI2 count.
If the pulse inputs are configured for a shaft encoder, a pulse rate is still calculated -
corresponding to rate change of level. A zero rate (“steady level”) will correspond to a 50%
analogue signal. The analogue signal will be more than 50% if the level is increasing, and
less than 50% if the level is decreasing. If an incremental shaft encoder is used, then the rate
may be scaled by scaling PRATE1. If a quadrature encoder is used, scale PRATE2. The
scaling value will determine both the 100% analogue signal (e.g. 20mA) and 0% signal (e.g.
4mA). For example, if a maximum pulse rate of 10Hz is configured, then the analogue
signal will be:
100% if the encoder increases at 10Hz 50% if the encoder pulse rate is 0
0% if the encoder decreases at 10Hz. 75% if the encoder increases at 5Hz
25% if the encoder decreases at 5Hz
Note that this is only true if the pulse inputs are configured for a shaft encoder. If standard
pulse inputs are used, then 0% analogue signal will correspond to zero pulse rate (0Hz).
The pulse rates are treated as analogue inputs and follow the rules for an analogue input as
described below.
2.4.5 Analogue Inputs
The analogue input can measure from 0 – 24mA or 0 – 10VDC. Current or voltage input can
be selected by an internal selector (refer Installation section of this manual). The mA input
can be used for conventional 4-20mA signals or 0-10mA or 0-20mA. The voltage input can
be used for 0-5 or 0-10VDC signals. The 505K unit is factory configured for a 4-20mA
signal, however the user can calibrate the unit for other ranges. The measurement resolution
is 12 bit.
The analogue input uses a “sample time” and “warm-up time” configured by the user. The
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505K Radio Telemetry Module User Manual
sample time (0 – 32727 sec or 9.1hours) “wakes” the 505K from sleep mode and turns on the
analogue loop supply. The “warm-up time” (0 – 100 seconds) allows the transducer to reach
rated accuracy before the 505K makes a measurement of the analogue signal.
For example, if the sample time is 30 minutes and the warm-up time is 10 seconds, then every
30 minutes, the 505K will turn on its analogue loop supply and after a further 10 seconds,
take a measurement of the analogue signal. After the measurement is taken, the 505K reverts
to sleep mode. The loop voltage available for a transducer is approx. 24VDC.
If the warm-up time is set to the same or more than the sample time, then the analogue loop
will be on continuously, and the 505K will measure the signal based on the sample time. For
example, if the sample time is 10 seconds, and the warm-up time 20 seconds, then the
analogue loop will be continuously active and a measurement made every 10 secs. If the
sample time is set to zero, then a measurement is made every cycle of the 505K - that is,
0.5 sec.
Note that continuous analogue loop operation will result in a short battery life if a battery
supply is used. A solar panel and battery supply is suitable.
If an externally powered analogue signal is connected, then the same measurement process as
described above occurs .
When the 505K takes a measurement, it will transmit the analogue value if the value has
changed by more than the pre-configured sensitivity since the last transmission. The
sensitivity can be configured from 0.1% to 75% with a default value of 3%. If the change in
the signal since the last transmitted value is less than the sensitivity, then the 505K will not
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transmit the analogue value.
The sensitivity value should be selected which is more than the normal analogue signal noise.
If the sensitivity is less than the signal noise, then the 505K will send a lot of un-necessary
transmissions, possibly resulting in jamming the radio channel.
An update transmission of the analogue value will be transmitted if the analogue value has not
been transmitted for during the user-configurable update period (10 seconds - 7 days). If an
update time of zero is selected, then no update messages will be sent.
If the update time expires since the last transmission, then the last measured value will be
transmitted - that is, a new measurement will not be taken. Normally the update time will be
much longer than the sample time. If the update time is less than the sample time, then update
messages may transmit the same value as the previous transmission, as a new measurement
has not yet been taken.
Overview:
• Measurements of the analogue signal are determined by the sample time and warm-up time
• Analogue value is transmitted if the measured value has increased by the configured
sensitivity amount since the last transmission
• Analogue value is transmitted if the input value has not been transmitted within the update
time (10 seconds – 7 days)
• There is no paralysis time for the analogue input.
2.4.6 Setpoint Status
The setpoint status is an internal status value, calculated by comparing the analogue input to
two configurable setpoint values. The setpoint status turns ON when the analogue input
moves below the low setpoint value, and turns OFF when it moves above the high setpoint
value. The high setpoint percentage must always be greater than, or equal to, the low set
point.
The internal setpoint status will be determined every time an analogue measurement is taken.
The setpoint status is treated as a digital signal and its value is transmitted according to the
rules for a digital input.
2.4.7 Supply Voltage
The 505K measures the supply voltage and stores it as an internal “analogue” value. The
range of the analogue value is 0 – 30 volts. The measurement is made every time the radio
transmits (the measured value is the “loaded” supply voltage) and the measurement is
transmitted based on the user-configurable update time - there are no change transmissions
for this value.
2.4.8 Low Supply Voltage Alarm (Supply LowVolts)
If the voltage of the power supply falls below the pre-configured alarm value, the internal low
voltage alarm will turn on. The 505K provides user-configurable high and low setpoints for
the supply voltage value. If the supply voltage falls below the low SP, then the Supply Low
Volts status will turn on. When the supply voltage increases above the high SP, the status
will turn off. The low SP should not be set less than 5.7V.
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505K Radio Telemetry Module User Manual
The Supply Low Volts is treated as a digital signal and its value is transmitted according to
the rules for a digital input.
2.4.9 Supply Failure
The 505K will stop operating if the supply voltage falls below 95% of the Supply LOV value.
Prior to shutting down, the 505K will store the values of the pulse counters in non-volatile
memory. The unit will restart when the supply voltage has increased to the configured high SP
value.
2.4.10 Communications Failure
The 505K cannot provide an indication that its transmitted messages have not been received
successfully.
This indication is however available at the receiving 105U by using the 105U Output Reset
on Comms Fail function. To use this function, map an input that is not being used on the
505K to a spare output on the 105U. The unused input can be an internal input such as the
Low Voltage status or Setpoint status, or even the analogue input as this can also be mapped
to a digital output. Configure the 505K so that the digital output at the 105U is normally on you can configure an input to output mapping to be inverted or direct.
If you configure a reset time to the 105U output, then this output will turn off if it has not
received an update message from the 505K within that time. The 105U output is effectively a
"Communications OK" output - on when communications are OK, and off during
communications failure. Note that the maximum output reset time at the 105U is 32 minutes,
so the update time for the 505K input must be less than this. It is generally a good idea to set
the update time to less than half of the reset time. Then, the 105U must fail to receive two
consecutive update messages - it is possible to miss one update message because of random
noise, but two consecutive failures means that there is a system failure.
For example, if you wish to have a failure alarm within 10 minutes of a system failure, set the
output reset time at the 105U to 10 minutes and the update time at the 505K to 4.5 minutes.
2.5 How to Design a Remote Monitoring System
2.5.1 Achieving reliable radio transmission
A system can theoretically have an unlimited number of 505K modules, but in practice, the
number is limited by the amount of radio traffic on one frequency in the system. When a
radio channel becomes unreliable because of radio traffic, then a second radio channel must
be used to increase the size of the system. This limit is not a function of the number of
modules, but the number of radio messages.
A system comprises 505K and 105U modules - each can transmit input signals. The 105U
can "hear" other radio messages, and will hold off transmitting a message until the radio
channel is clear. The 505K module cannot, and there is a possibility that an individual
transmission will clash with another transmission, and both transmissions will be corrupted.
This possibility increases as the density of transmissions increases. Configuring the retransmit feature (transmission of each message several times) will increase the chance of each
message being received successfully, but will increase the overall density of radio traffic.
For large systems, a compromise is required between the number of re-transmissions, and the
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update times for each input. High priority inputs should have shorter update times than lower
priority inputs.
The peak transmission density should be calculated for large systems. These values are
calculated by determining the number of transmissions from inputs changing value and the
number of update transmissions per hour.
The probability of success for an individual message depends on the transmission density and
the number of re-transmissions for each message. This is shown in the following graph:
Prob a bility of s ucc ess ful t ra n sm issio n
100 %
90%
80%
70%
60%
50%
40%
30%
20%
10 %
0%
0 100 0 200 0 3000
M essa g es Pe r Ho ur
Trans miss ions
pe r m essage
1
2
3
4
5
This assumes that the radio path is reliable and that there is no other radio users on this radio
channel. If intermediate repeaters are used, then each repeated message should be counted as
another message.
We suggest that you use two transmissions per message - with a higher number for a small
number of high priority inputs.
In addition to the above comments, you need to consider the affect of re-transmissions on
other messages being transmitted from the same 505K module. Once a 505K starts
transmitting a message, all transmissions for this message must be complete before another
transmission can start. The time between retransmissions of the same message is a random
time between 0.5 and 4 seconds. For example, if a module is configured to transmit each
message 5 times, then each message will take up to 16 seconds. Another message cannot be
transmitted until the previous message has finished. In the above example, the maximum
number of messages which can be transmitted reliably is approx 4 per minute. If more
messages are required, then a lower number of re-transmissions should be selected.
2.5.2 How far will the radio transmit?
The 505K will operate reliably over approx. 5km line-of-sight. The distance that can be
reliably achieved will vary with each application and is dependent on the following factors:
• Type and location of antennas (the higher an antenna is, the further it will transmit)
• Amount of radio interference from other transmitters or radio “noise”
• Obstructions such as buildings, hills or trees in the radio path.
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