Synapse RTU-ADC8 User manual

RTU-ADC8 –8 Channel Analogue In
Modbus RTU Module
Documentation Issue 1.4

Features
8 Channels
Each channel selectable as 4-20mA or 0-10V/0-2V DC operating mode (via internal “Push-
On” jumper link settings)
Software selectable per-channel 12/14/16/18bit resolution
Software Modbus registers for
-Live Channel Reading
-Average Channel reading (software selectable as over 4/8/16 readings)
-Max channel reading*
-Min channel reading*
-Channel Resolution configuration setting
-Short/Med/Long average configuration setting
-Baud Rate configuration setting
Modbus Address selection via external “Push-On” jumper link setting
Fast Modbus poll rates <100ms
Factory Reset Via “Push-On” link setting
Integrated Watchdog and Power “Brown-Out” detect and correct
Internal RS485 Bus Pull and Termination Resistors
*These threshold registers are user writeable so a reading can be taken, the registers written back
to, either to zero out or set a new threshold, the system will check new readings against these values
and overwrite if the threshold has been exceeded in the respective direction.

Safety and ESD Precautions
Before first use, refer to this manual.
Before first use, make sure that all cables are connected properly
Please ensure proper working conditions, according to the device specifications
e.g. Supply voltage, ambient temperature, maximum power consumption
requirements.
Ensure all wiring and connector terminals are securely fastened so as to avoid short
circuits or other such damage.
Before making any modifications to wiring connections or PCB settings, turn off
the power supply.
Note: This equipment has been tested and found to comply with the limits for a
Class A digital device, pursuant to part 15 of the FCC Rules. These limits are
designed to provide reasonable protection against harmful interference when the
equipment is operated in a commercial environment. This equipment generates,
uses, and can radiate radio frequency energy and, if not installed and used in
accordance with the instruction manual, may cause harmful interference to radio
communications. Operation of this equipment in a residential area is likely to cause
harmful interference in which case the user will be required to correct the
interference at his own expense.
Caution - Component damage. Circuit boards contain electronic components that
are extremely sensitive to static electricity. Ordinary amounts of static electricity
from clothing or the work environment can destroy the components located on
these devices.
Do not touch the components without antistatic precautions, especially along the
connector edges.

Specifications
Power Supply
Voltage
6-28 VDC
Maximum Current
10mA @12V Max
Analogue IO
No of inputs
8
Input Range (Voltage Mode)
0–10V / 0-2V
Input Range (Current Mode)
0–20mA
Resolution
12/14/16/18Bit
Accuracy
±0.2% or better
Environmental Conditions
Operating Temperature
-20°C to +70°C
Storage Temperature
-40°C to +85°C
Humidity
0 .. 90 %
(non-condensing)
Isolation
Isolation
1500 Vrms
(Between CPU/Power and Analogue Inputs)
Dimensions
Height/ Length
120x101 mm
Communication
Protocol
Modbus RTU
Baud
9600-57600
(19200 Factory Default)
Address
1-31
EMC
Rating
Class A (Industrial)
Immunity
EN 61000-6-2
Emissions
EN 61000-6-4
IP
IP Rating
IP20

RTU Module Pin Out
1 –0V
2 –DC IN
8 –CH2 -
7 –CH2 +
6 –CH1 -
5 –CH1 +
4 –CH4 -
3 –CH4 +
2 –CH3 -
1 –CH3 +
3 –0V
2 –RS485 B
1 –RS485 A
QUICK COM
1 –CH7 +
2 –CH7 -
3 –CH8 +
4 –CH8 -
5 –CH5 +
6 –CH5 -
7 –CH6 +
8 –CH6 -
Note that all channel negative terminals are connected together
All 4-20mA inputs are protected from over voltage/current

Status LEDs & Modbus ID
Modbus Address ID Link Setting
Link No
Address Setting
1
Modbus Address +1
2
Modbus Address +2
3
Modbus Address +4
4
Modbus Address +8
5
Modbus Address +16
No Links
Use factory defaults*
* Factory Default setting :
Address Id = 1
Baud Rate = 19200 8N1
All NVRAM values reset to zero (where applicable)
Top
Bottom
Green
Power On
Modbus Rx
Red
-
Modbus Tx
1
5
Status LEDs

Modbus Address ID Selection Link
Addr
5
4
3
2
1
0*
OFF
OFF
OFF
OFF
OFF
1
OFF
OFF
OFF
OFF
ON
2
OFF
OFF
OFF
ON
OFF
3
OFF
OFF
OFF
ON
ON
4
OFF
OFF
ON
OFF
OFF
5
OFF
OFF
ON
OFF
ON
6
OFF
OFF
ON
ON
OFF
7
OFF
OFF
ON
ON
ON
8
OFF
ON
OFF
OFF
OFF
9
OFF
ON
OFF
OFF
ON
10
OFF
ON
OFF
ON
OFF
11
OFF
ON
OFF
ON
ON
12
OFF
ON
ON
OFF
OFF
13
OFF
ON
ON
OFF
ON
14
OFF
ON
ON
ON
OFF
15
OFF
ON
ON
ON
ON
16
ON
OFF
OFF
OFF
OFF
17
ON
OFF
OFF
OFF
ON
18
ON
OFF
OFF
ON
OFF
19
ON
OFF
OFF
ON
ON
20
ON
OFF
ON
OFF
OFF
21
ON
OFF
ON
OFF
ON
22
ON
OFF
ON
ON
OFF
23
ON
OFF
ON
ON
ON
24
ON
ON
OFF
OFF
OFF
25
ON
ON
OFF
OFF
ON
26
ON
ON
OFF
ON
OFF
27
ON
ON
OFF
ON
ON
28
ON
ON
ON
OFF
OFF
29
ON
ON
ON
OFF
ON
30
ON
ON
ON
ON
OFF
31
ON
ON
ON
ON
ON
* Invokes Factory Default setting:
Address Id = 1
Baud Rate = 19200 8N1
All NVRAM values reset to zero (where applicable)

Current/Voltage Input Mode Selection
To change a channels operational mode between 4-20mA Current Loop input or 0-10V Voltage Input
a set of internal push-on jumper links must be adjusted
Each channel may be set according to the link setting below, the factory default position is 4-20mA
mode on all channels.

RS485 Bus Option Links
Fit links below to enable the function shown
RS485 Low Bus Pull
RS485 High Bus Pull
120ΩTermination
Resistor
Important: Only one set of bus data line pulls should be active,
either at the master side or on a single slave
Important: Termination resistors should only be enabled at far
ends of bus

RS485 Bus Connection
RTU Plug RS485 Wiring
RS485 A/+
RS485 B/-
RS485 0V
Shield –Only connect on one end of cable!
Belden 9481 (120Ω Cable)
Modbus
Master
RS485 A/+
RS485 B/-
RTU
Module
RTU
Module
RTU
Module
120Ω
Termination
High Bus Pull
Low Bus Pull
120Ω
Termination

Current Loop & Voltage Input Connections
Voltage Input Mode
Current Loop Mode
Arrows show current flow direction
Low side configuration is preferred and recommended
Sensor
0V
+24V
High side configuration
Low side configuration
0V
+24V
Sensor
Sensor
0V
0-10V

Modbus Registers –Readings
Register
Type
Read/Wite
Description
40001
32Bit IEEE754 Float
(Big Endian)
Read Only
ADC Channel 1 Live Reading
40003
32Bit IEEE754 Float
Read Only
ADC Channel 2 Live Reading
40005
32Bit IEEE754 Float
Read Only
ADC Channel 3 Live Reading
40007
32Bit IEEE754 Float
Read Only
ADC Channel 4 Live Reading
40009
32Bit IEEE754 Float
Read Only
ADC Channel 5 Live Reading
40011
32Bit IEEE754 Float
Read Only
ADC Channel 6 Live Reading
40013
32Bit IEEE754 Float
Read Only
ADC Channel 7 Live Reading
40015
32Bit IEEE754 Float
Read Only
ADC Channel 8 Live Reading
40017
32Bit IEEE754 Float
Read Only
ADC Channel 1 Average Reading
40019
32Bit IEEE754 Float
Read Only
ADC Channel 2 Average Reading
40021
32Bit IEEE754 Float
Read Only
ADC Channel 3 Average Reading
40023
32Bit IEEE754 Float
Read Only
ADC Channel 4 Average Reading
40025
32Bit IEEE754 Float
Read Only
ADC Channel 5 Average Reading
40027
32Bit IEEE754 Float
Read Only
ADC Channel 6 Average Reading
40029
32Bit IEEE754 Float
Read Only
ADC Channel 7 Average Reading
40031
32Bit IEEE754 Float
Read Only
ADC Channel 8 Average Reading
40033
32Bit IEEE754 Float
Read/Write
ADC Channel 1 Maximum Reading
40035
32Bit IEEE754 Float
Read/Write
ADC Channel 2 Maximum Reading
40037
32Bit IEEE754 Float
Read/Write
ADC Channel 3 Maximum Reading
40039
32Bit IEEE754 Float
Read/Write
ADC Channel 4 Maximum Reading
40041
32Bit IEEE754 Float
Read/Write
ADC Channel 5 Maximum Reading
40043
32Bit IEEE754 Float
Read/Write
ADC Channel 6 Maximum Reading
40045
32Bit IEEE754 Float
Read/Write
ADC Channel 7 Maximum Reading
40047
32Bit IEEE754 Float
Read/Write
ADC Channel 8 Maximum Reading
40049
32Bit IEEE754 Float
Read/Write
ADC Channel 1 Minimum Reading
40051
32Bit IEEE754 Float
Read/Write
ADC Channel 2 Minimum Reading
40053
32Bit IEEE754 Float
Read/Write
ADC Channel 3 Minimum Reading
40055
32Bit IEEE754 Float
Read/Write
ADC Channel 4 Minimum Reading
40057
32Bit IEEE754 Float
Read/Write
ADC Channel 5 Minimum Reading
40059
32Bit IEEE754 Float
Read/Write
ADC Channel 6 Minimum Reading
40061
32Bit IEEE754 Float
Read/Write
ADC Channel 7 Minimum Reading
40063
32Bit IEEE754 Float
Read/Write
ADC Channel 8 Minimum Reading
To read one or more registers you should use Modbus function code 3 –Read holding registers (4x
Range)
To write one or more registers you should use Modbus function code 16 –Write multiple registers
Only function codes 0x03 (FC03) and 0x10 (FC16) are accepted by the module

Note :
Channel Maximum/Minimum registers record the peek value, i.e. the highest/lowest values seen by
the ADC, each subsequent live reading is tested against this value with the register value being
updated if the live reading exceeds the threshold value stored here.
Writing a value to the Max/Min registers will set a new threshold value for testing against.
Modbus Registers –Configuration
Register
Type
Read/Write
Description
40065
16 Bit
Read/Write
ADC Channel 1 Resolution
40066
16 Bit
Read/Write
ADC Channel 2 Resolution
40067
16 Bit
Read/Write
ADC Channel 3 Resolution
40068
16 Bit
Read/Write
ADC Channel 4 Resolution
40069
16 Bit
Read/Write
ADC Channel 5 Resolution
40070
16 Bit
Read/Write
ADC Channel 6 Resolution
40071
16 Bit
Read/Write
ADC Channel 7 Resolution
40072
16 Bit
Read/Write
ADC Channel 8 Resolution
40073
16 Bit
Read/Write
ADC Average Period
40074
16 Bit
Read/Write
Modbus Baud Rate Setting
40075
16 Bit
Read/Write
Modbus Float/Raw Readings Mode
40076
16 Bit
Read/Write
Save Settings to NVRAM
40065-40072 Channel resolution
This is a per channel setting with the following options set as the register value as below, the higher
the resolution the longer the channel sample time.
Register Value
Channel Setting
0
16 Bit
1
12 Bit
2
14 Bit
3
16 Bit
4
18 Bit

40073 - Rolling Average
This sets the number of readings used for the rolling average, if dealing with noisy or rapidly
fluctuating signals this filter will help to stabilise the reading.
Register Value
Setting
0
8 Readings
1
4 Readings
2
8 Readings
3
16 Readings
40074 - Modbus Baud Rate
This sets the serial baud rate of the unit
Register Value
Setting
0
19200
1
9600
2
14400
3
19200
4
38400
5
57600
40075 - Modbus Float/Raw Readings Mode
This sets whether the RTU unit calculates and presents scaled floating point readings or raw ADC
values.
Register Value
Setting
0
Float Mode
1
Raw Mode
40075 - Save Settings to NVRAM
Writing 255 to this register will cause the system to save the current configuration and reboot the
unit, this is required if any of the parameters have changed e.g. baud rate or channel resolution.

Decoding RAW ADC Modbus Readings
The values stored by the RTU unit for Live/Average/Max/Min values are usually presented as 32Bit
IEE754 Float, having an accuracy of 6 significant figures, if the ADC unit is configured to output the
raw ADC readings greater accuracy can be obtained.
To convert the raw readings to voltage/mA use the below process using the appropriate scaler
depending on the ADC channel resolution setting.
The ADC readings are stored as 32bit (2 x 16bit registers) in big endian format
Resolution Setting
Scaler
12Bit
0.001
14Bit
0.00025
16Bit
0.0000625
18Bit
0.000015625
Worked example
Mode : 16 Bit
Modbus Reading : 20709
Raw ADC Voltage = 20709 * 0.0000625 = 1.2943125
4-20mA Mode
4mA = 0.4V & 20mA = 2V
To convert to mA multiply Raw ADC value by 10
e.g. 1.2943125 * 10 = 12.943125mA
0-10V Mode
Multiply Voltage reading by 5 to get scaled 0-10V value
e.g. 1.2943125 * 5 = 6.4715625V

Software Support
Open-Source code samples can be downloaded from the GitHub repositories below :
RTU Specific Configuration Tool
https://github.com/synapsertu/rtu-ai8
Multi RTU module Logger
https://github.com/synapsertu/rtu-log
Modbus Utilities
The following windows and Linux command line utilities are useful for development
Windows/Linux x86 Binary
https://www.modbusdriver.com/modpoll.html
Raspberry Pi/Linux
https://github.com/epsilonrt/mbpoll
*Note that mbpoll does not use FC16 for Modbus writes