PST 53041E Digital Humidity and Temperature Probe User Manual

PST 53041E Digital Humidity and Temperature Probe User Manual

Rotronic Modbus – Digital Communication

Mod bus is a popular communication protocol used in industrial automation to exchange data between devices such as PLCs, sensors, and actuators. Mod bus can be over Ethernet (known as Modbus TCP) using standard patch leads or over RS-485 and RS-232 (known as Mod bus RTU) using twisted pair cables.

This guidance is intended for users who have not worked with Modbus and need a step-by-step instruction on how to connect the HCD-S-MOD (RMS-HCD-S & E2-05XX- MOD) to a computer and getting started with read out data through RS-485 with Mod bus R T U protocol:

Delivery Package

• R M S-H CD-S
• E 2-05 X X-MOD

List of used materials

• R M S-H C D-S
• E 2-05 XX-MOD
• AC 3001
• Luster terminal (3 pol)
• USB-R S 485-WE-1800-B T
• Mod bus Master software
• R M S-CONFIG
• Hex Converter

Why use Modbus over RS-485?

Modbus RTU networks are predominantly used due to the ease and reduced cost of adding many devices via a single “bus cable” (unlike analogue or ethernet that requires a direct cable to every device). With Modbus RTU networks you can also easily add additional devices at any point along the bus cable. Only a single PLC device is required to communicate with potentially up to 247 devices presenting a huge cost saving compared to analog signals. Finally, by using digital vs analog thereis no signal degradation or error and you are also able to receive additional information such as device and probe serial numbers, units & error codes.

Interface

Per default the RM S- H C D-S has an U A RT service interface which is converted by the E2-0 5 XX -MOD BUS into RS-485. The third-party device US-RS 485-WE-1800-BT so then convert the RS-485 signal to USB:

Device| Interface Analog| Digital UART| +AC3001| +E2-05XX­MOD’| Communication Modbus| RTU| Parameter Hum/Temp| Cost Budget
---|---|---|---|---|---|---|---|---
RMS-HCD-S| No| USB| RS-485| Yes| °/orh & °C| SS

1 Note: Rotronic can only support the RMS-HCD-S in combination with the cable E2-05XX-MOD in use.
Schematic structure

Wiring
Wiring of the setup

1. Connect the RMS-HCD-S with the E2-05XX-MOD
2. Connect the E2-05XX-MOD with the luster terminal
3. Connect the USB-RS485-WE-1800-BT with the luster terminal
4. Connect the USB-RS485-WE-1800-BT with the USB to computer

Specification

1. RMS-HCD-S
   

2. E2-05XX-MOD
   

3. USB-RS485-WE-1800-BT
   

Setup the Modbus address
Review the RMS-HCD-S Modbus address of the RMS-HCD-S probe with the RMS-CONFIG software. Plug the RMS-HCD-S into the AC3001 cable and add a local device, per default the probe address is 247:

Modbus Master software

Modbus Tool-Master
The Modbus Master software is a third-party software which we can use to start communication with the connected RMS-HCD-S. To communicate with the systems, the following information must be set up:

1. Mod bus RTU
2. Baud rate 19°200
3. Parity: none
4. Data bits: 8 o Lode
5. Stop bits: 1 R
6. Slave ID: 247

Port Name
Before the communication can be started, the port name must be determined. For this, you can check the ports within the Device-Manager on your local computer:

Connect the Modbus Master software

Read out data
The Modbus address overview can be reviewed here: MODBUS
The addresses 31000 and 31004 are the humidity & temperature values.
NOTE : RS485 address is the register address -1!
Add the start address 31000, Size 4, Display Format hex, press Apply and then Read Input register:


Data format received
The data format, or also called swap mode. The standard setting is 0x0001 with target bytesd ¢ b a:

31001

|

[c d] 5e42

Interpretation of received data

The received data in hex format must be converted into a float format with decimal values.
We use a third-party calculator which can be downloaded under Floating Point to Hex Converter (gregstoll.com):

The hex value 0x425eced2 is in decimal floating data format 55.7 %rh.

Read out temperature values
The addresses 31003 and 31004 are the humidity values.
NOTE: RS485 address is the register address -1!
Add the start address 31002, Size 2, Display Format hex, press Apply and then Read Input register:

31001

|

[c d] 5e42

The hex value Oxea5cbf4l is in decimal floating data format 23.9 °C

Change data format
Before we can change the data format, we must read out the actual byte-swap format.
The addresses 40001 show the actual byte-swap format:
NOTE : RS 485 address is the register address -1!

Change to data format to 0x0000
Add the start address 40001, Size 1, Display Format hex, write into the address box a “0”, press Apply and then Write single register:

Read again the holding register of address 40001 and system has changed data format:

Read out humidity values again

31001

| [cd] 4c42
Target Bytes

51.24 %r h

Rotronic Modbus wall
The Rotronic test application includes all Rotronic devices that are Modbus RTU capable. The testing wall is designed in such a way, that the devices used are constantly evaluated. The transmission rate (error rate) can be tracked via the integrated monitor.

Rotronic Modbus application wall
Device list

• 2x PF4/PF5
• 3x HF5A-Digital
• 3xRMS-HCD-S
• 3xRMS-HCD-IC102
• 3xRMS-TCD-S-001

Modbus Master

• B&RX20CP1583 with RS-485 module X20IF1030

Bus cable

• VOLLTRON-Twist CY A 2X2X0,25

Rotronic Modbus wall
To ensure smooth communication between Modbus devices on a network, it is crucial that they all have the same communication parameters and unique Modbus device addresses. During initial setup each Rotronic device was programmed individually with a unique address. Rotronic Modbus protocol:
Hardware Overview > Sensors and Probes > HCD-Sx > MODBUS (rotronic.com)
The Modbus protocol utilizes function codes to exchange data between the master and slave devices and each vendor may have different register addresses for the same data due to the vendor-specific nature of Modbus registers. The Rotronic devices only support half-duplex operation, half-duplex is acommunication mode which two devices can transmit and receive data, but not simultaneously. In other words, communication is bidirectional but canoccurin one direction at a time. The SPS controller is the master and the Rotronic devices are the slaves. When the master requests, the first device can answer, then the second device, and so on.

Modbus cables can support different distances depending on the type of transmission and environment. The distance a Modbus cable can span without amplification depends on factors such as cable type, cable quality, transmission rate, voltage level, ambient temperature, and electromagnetic interference (EMI). For RS-485 Modbus communication using differential signal transmission, cable distances of up to 1200 meters can be achieved.

Up to 1200-meter cables
The dimensionless of terminating and bias resistors:

We have chosen 1 kQ as bias resistors and 390 Q respective 220 Q AS terminating resistors.

Polling interval
The polling interval is defined by the slowest device in this case the PF4/PF5 with 400 ms.
In this application we have 14 devices connected and one polling cycle takes approx. 5.6 seconds.

Polling cycle = Number of devices * Polling interval

Evaluation of the data The Modbus wall is in continuous operation and is evaluated with an additional software. The wall sim- ulates pressure changes several times a day, which is realized by a fan. Everyday some devices are switched off and turned on again. In addition, the Rotronic devices are continuously interrogated, and the response behavior is tracked and evaluated:

Out of more than 300’000 requests, only 8 responses were not received, which corresponds to an error rate of 0.002%.
Monitoring of all devices and values and error counting

Rotronic Modbus device list
Rotronic devices are designed to monitor and control various parameters, such as humidity, temperatures, and differential pressure. The new generation of probes and transmitters are capable to measure these parameters and a Modbus interface for communication with other devices on the network

Device
Analog| Interface Communication      Parameter+E2-05XX- Hum/Temp/Digital             +AC3001 ModbusMOD Pressure|

Cost

Budget

---|---|---
RMS-HCD-S| No| UART               USB      RS-485| Yes| RTU| %rh & °C| $S
RMS-HCD-IC          No| UART| USB             RS-485             Yes| RTU| %rh & °C| $$$
R MS -TC D -S| No| UART| USB            RS-485| Yes| RTU| °C| $
PCD-S                       No| UART| USB             RS-485             Yes| RTU| Pa| 5$
HC2A-S| 0…1V| UART| USB            RS-485| Yes| R0-ASCII %rh & °C| $5
HC2A IC                 0…1V| UART| USB             RS-485             Yes| RO-ASCII    %rh & °C| $$$
PCMini52| 0…1/5/10V| RS-485| No                   No| Yes| RTU       %rh & °C| $
PC62 & PC62V Device| 0…1/5/10V| RS-485| No                 No Yes| RTU               %rh & °C| SS
Probe Type| Interface
screw-terminal| Interface POE LAN (RJ-45)| Commu- nication| Parameter| Cost
| | Analog                 Digital Digital| | Mod bus| Hum/Temp/ Pressure| Budget
HF3                    Fixed| Yes                     No                No No| No| %rh & °C| $
1-1F5| Interchange| Yes                     RS-485 Yes| No| RO-ASCII| %rh & °C| 5$
PF4/PF5       InterchangeI| Yes| RS-485| Yes                      Yes| RTU &TCP| °/orh & °C & Pa| $$$

Additional Guidance
For customers who do not have experience with digital communication, the Rotronic RMS online manual has additional pages with instructions on how to integrate the Rotronic device and start communication. For more detailed discussion please contact the Rotronic PM team. Help > Practical Topics > Understanding MODBUS > Guidance for MODBUS Communication with the RMS-HCD Digital Probe (rotronic.com)
Conclusion
Customers increasingly seek the most cost effective and efficient solution. Digital communications can present many benefits to our customers. Understanding the basics of Modbus network is vital to support customers and their products.

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