RKC PZ900 temperature controller

[GerdW]

Hi arienai,

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@arienai wrote:

As mentioned in 5-13, there is a warning for the decimal numbers, as MODBUS does not recognize data with decimal point.

Then, I cannot understand how PZ900 can understand a set value 298.5 for example. There is 5 digits and 4 bytes data, so it is OK, but how PZ900 can interpret the decimal part ? 

So here is back to orignal question about the difference between programming in single word rather than double word : is single word prevent decimal settings ? 

Further, ...  the MODBUS data mapping will break my brain ... for sure ! 

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Maybe it would help when you would learn about Modbus first?

There are surely documents at Wikipedia…

Or you start reading the official website, they offer a huge amount of information!

Most of the questions in your last post are handled inside the Modbus libraries I mentioned before, so you don't need to worry about. All you need to worry about is the way how Modbus handles values/datatype of more than 2 byte size, like your single/double float data: you need to convert them (aka typecast) to an array of U16 values…

[arienai]

Thank you GerdW

I just had a look to the modbus.org web site ... clearly, the purpose of using Modbus is far away from my needs. So such PZ900 has too many functions that are useless for my application. 

So I just need to set a temperature, and read temperature. That is pretty much all I need.

Then an example of 1 instruction of PZ900 using Serial Modbus library , will be more than helpful.  

By understanding an example, I can work to build all other necessary commands. This is the purpose of sharing my concern on this forum. And I am happy to get some help from you. 

[GerdW]

Hi arenai,

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@arienai wrote:

Then an example of 1 instruction of PZ900 using Serial Modbus library , will be more than helpful.  

By understanding an example, I can work to build all other necessary commands.

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Did you install a Modbus library from VIPM?

If you have done that: open their example VIs. There will be an example showing you how to read a value from a Modbus device.

Try to read registers 0 & 1 to get the PV (MeasuredValue, see page 6-8). I guess you need to a function named "ReadHoldingRegister", it's some time since I used Modbus on that level.

[arienai]

Dear GerdW,

yes the library is already installed, I already opened the example (before your answer). The ReadHoldingRegister is also there. 

Before testing this MODBUS com, I wanted to be sure about the correct instruction to be sent.

I have another option, plan B, in case such MODBUS com is too complicated. Plan B as follow. The PZ900 intends to 1- collect temperature from a thermocouple, 2- send instructions to a power source in order to heat up the hardware (hot plate).

I already succeeded to control the power source, to set current/voltage using Labview. 

Now, I am just trying to read temperature from PZ900 using MODBUS protocol, which is completely absurd since PZ900 embeds functionalities much more complex for intelligent control of the power source through PID.

But Labview has also PID functions (on the forum, I read your answers to someone who had troubles with PID settings)

        PID for temperature control               

So Plan B is simply to stop using PZ900, connect the thermocouple to a DMM2110 (Keysight) which has thermocouple input and easy reading of temperature, then use labview PID eventually, then set the power source accordingly with a feedback control on the thermocouple readings. This way is easier to me, despite the fact that PZ900 which is embedded in the machine, will not be used anymore. 

Before Plan B, let's try MODBUS for a while. 

[arienai]

today, I set the PZ900 for MODBUS communication (CMPS = 1, ADD=1). 

I opened the MODBUS library example, as you suggested. 

In this example, the slave address (on top) is localhost. Port is 502. But this is TCP settings, and I am using port COM10 through USB cable. 

So I need to adapt the example for MODBUS SERIAL, isn't it ? 

I did. I replaced the polymorphic selector from "new TCP master" to "new  serial Master". 

It seems to connect. 

Now I have to play with Coils, Holding Registers and so on. 

[arienai]

I attached the modbus example that I modified for SERIAL. 

I downloaded a software called Serial Port Monitor. 

I run the PRO-TEM software from RKC, that is communicating with PZ900 through COM-K2 module, from PC Win10-64 via USB port. 

I attached the results of Serial Port Monitor, when I started monitoring the temperature using PRO-TEM on port COM10.

Basically, PRO-TEM is sending the instructions write/read to PZ900. So I could see what the commands should look like. 

The tempeature was 19.3 degree C at the moment of the recording. I attached a screenshot. 

Now, I would like to set the Labview modbus example with the correct data. For this purpose, I need to fill correctly the HoldingRegisters. 

I succeeded to CONNECT.

This is my actual problem. In the example, there are 8 rows to be filled in Holdings Registers.  

I put   04 30 30 4F 32 05  then set Holding Registers. It is HEX but I cannot set 04. It is displayed as 4 rather than 04, EVEN I set correctly the entry of this input properties to HEX.

[arienai]

Dear GerdW,

would it be possible for you to pick up an instruction from the manual, and implement 1 one sub-vi of the modbus serial library ? Just for testing it from my side. 

[arienai]

Dear GerdW,

update : just to let you know 

I called RKC yesterday, I am not sure to have understood everything as it was in Japanese, but I have understood that to allow serial modbus communication with PZ900, the hardware configuration must be revised. That why I failed using any vi from NI labview modbus library. 

They said that using COM-K2 allows the communication with PRO-TEM software only, and prevents communication with serial port ... 

Then what I have to do, is 1) to remove COM-K2 unit, 2) to plug slots 32,33,34 on the rear panel of PZ900 is order to become in RS-422 configuration. Then it might be to use modbus library. 

[arienai]

I just share my experience : I removed RKC PZ900 from my setup, and I replaced it with a Eurotherm 3504. 

RKC PZ900 is compact, and can be set easily using free PROTEM2 software through COM-K2 unit (RS to usb converter). It is also quite cheap in the market. But the PID are not so much accurate. And there is no labview libraries. 

Eurotherm 3504 has better PID, and Labview libraries. It is a little bit more expensive, all functions/parameters are accessible through the well establish iTool software. 

Also, I would like to share the fact that RKC Japan had never answered to my emails for technical support, first time to have such experience in Japan ...