Alicat Mass Flow Control and RedLion

[OkiePC]

I think Dan has nailed it by stating that just because it has RS-485 doesn't mean it supports Modbus. This combined with the fact that the node address shows up as alphabetic.

 

[Kevin_G]

Hi, My name is Kevin, and I am an applications engineer for Alicat. This post has been brought to my attention and I am sorry to hear that you have been having trouble interfacing with an Alicat device that was purchased with the optional Modbus RTU over RS-485 (and even more sorry that the calls you placed with us were not helpful).

Similar to what others have posted, the first thing that we want to make sure of is that the wiring between the Alicat and the PLC is properly established. The MFC manuals should contain all pin-outs that are sold except for the ones specifically requested to be customized by the customer (pin-out type can be found in the part number, such as "DB9M" or "DB9R"). The one point of potential confusion I see for the "DB9M" pin-out specification, which is a male 9 pin connector using our standard pin-out (and I can look into getting our manuals altered if this is indeed a point of confusion). Chances are very good that your device is using the default Alicat DB9 pin-out, as I am showing that all but 2 devices made in 2014 with both Modbus over RS-485 and a DB9 connector have either used the DB9 or DB9M pin-out configuration.

The 485(+), 485(-), and ground must all be wired to the appropriate pins and will likely require a custom cable if you do not have access to screw terminal ports on the RedLion (because the pin-outs of the 9 pin connectors are not intended for use directly connecting to a 9 pin serial port on a PC/PLC).

The ASCII unit ID and the Modbus unit ID are separate things, and the device may show an ASCII unit ID of "A" but the Modbus ID is set to 1 by default.

As for the registers that you can read or write to, you may be able to get away with leaving off the 40000 (or in this case 400000) prefix and just entering something like 2053 or 2042 (as stated by in a prevuous comment). The Alicat Modbus RTU allows for only the two function codes to be called: function 03 for reading holding registers and function 16 for writing to multiple registers.

Additional info that may prove useful: When reading/writing to Alicat Modbus registers, the PLC should be indexed as base 1 to avoid reading and writing to the improper registers. I have also seen customers have issues if the data registers that use the two 16 bit registers are not decoded properly as a 32 bit float, so I would strongly second the recommendation to verify the temperature reading that was brought up in a previous post once you get it working.

If you would like to email me directly on the matter, I can be reached at [email protected]. Please let me know either through this forum or by email if you were able to get this up and running or if you have any questions, and I will do my best to assist.

 

[ceilingwalker]

Make 12 devices in the Red Lion. Use drop numbers 1-12. Add one tag and copy it to each of them. Put all twelve tags on a screen. See what you get.

Swap the comms + and - wires. See if anything changes.

If the device has LEDs for the RS485 port, you may be able to tell something from them. When they are backwards, you may see only a receive LED or a send LED light up. When correct, you may see rapid blips on both of them.

Technically, 2-wire RS485 is supposed to be three wire if you counted the signal common.

I tried this as you recommended, and I still get the "---". I am still not convinced wiring is correct. Even the cable has a tag that shows what wire lands on, but still nothing. I know the RedLion is polling, I can see that much of it.

 

[ceilingwalker]

1) Modbus is an option. RS-485 does not necessarily mean Modbus. It could mean 'streaming'. How do you know this specific unit talks Modbus?

Part#MCRH-5000SLPM-O-485-Modbus-IP66X

 

[ceilingwalker]

4) Why do you think that the user manual that shows the pinouts for RS-485 is incorrect? Why aren't pins 3, 5, and 8 on the 8 pin DIN connector the RS-485 lines?

Because the manual that came with it shows 5 different pin outs for the DB9 connector.

 

[ceilingwalker]

grumble, grumble, can't copy correctly. Should be:

starting at (4)02042 [or (4)02041 or (4)02043 when you test for a one offset addressing issue]

Thank you. I will try it now.

 

[ceilingwalker]

If it were me, I'd be polling with Modscan so I could see the additional feedback, like "no connection" or "time out".

I downloaded Modscan but am learning how to use it and I am not sure how I can use it, going through the RedLion.

 

[Kevin_G]

Part#MCRH-5000SLPM-O-485-Modbus-IP66X

Judging by the part number, the pin-out would be the circular 6 pin locking industrial connector on page 85 of this manual: http://www.alicat.com/documents/manuals/Gas_Flow_Controller_Manual.pdf (default for the "-X" units will be the locking 6 pin connector, for which there is only one version). Looking at the connector on the top of the Alicat, does it have only 6 pins?

If you are worried that a previous configuration that you may have tried could have damaged the RS-485 circuitry and may be preventing communication, you can probe the resistance between the 485 (+) and 485 (-) terminals with the device unpowered and unplugged. A device that has an undamaged RS-485 card installed should have a resistance across these 2 pins of about 255 kOhms. If the resistance is much smaller than this (such as ~130 kOhms), then the 485 board may have been damaged and causing you to be unable to communicate with the PLC.

 

[danw]

I downloaded Modscan but am learning how to use it and I am not sure how I can use it, going through the RedLion.

Modscan is an alternative master to the RedLion. You use it on its own.

1. The first task, page setup:

Address = 2042
Length = 4 (registers)
Device ID = 1
Modbus Point Type = 03: Holding Register(s)

2. Pick one of the 32 bit floating point 'format' buttons
Four Binary buttons: 011, 10, I, oX
two 32 bit Floating Point buttons: 32 Floating Pt or 32(red slash) Swapped FP
Two 64 bit Floating point buttons: 64 Double or 64 (red slash) Swapped Dble

In the screen shot above, 32 FP is selected (depressed)

3. Attempt connection

Connection > Connect > Connection details window

Use the dropdown menu to select "Direct Connection to COM x"; whichever COM port the USB/serial converter installs on (Windows control panel > Device Manager > Ports)
Baud Rate =
Word Length = 8,
Parity,
Stop bit = 1

Protocol Selections button > Modbus Protocol Selections window

Transmission Mode Standard = RTU
Daniel etc = none enabled
Slave response = 1000mS
Delay Between Polls = 1000mS
no force
OK
OK

See what happens when you attempt to connect.
[FONT=&quot]Closing out the Connection dialog boxes attempts connection.[/FONT]

[FONT=&quot]If there’s no RS-485 connection, you’ll get the "Device Not Connected" error.[/FONT]
[FONT=&quot]
[/FONT][FONT=&quot]If it thinks it sent something to a possibly valid address, you’ll get a timeout message[/FONT]
[FONT=&quot]
[/FONT][FONT=&quot]Obviously, the devices need to be wired and powered.[/FONT]
[FONT=&quot]If it thinks it sent something to a possibly valid address, you’ll get a timeout message[/FONT]
[FONT=&quot]Obviously, the devices need to be wired and powered.[/FONT]

 

[ceilingwalker]

The 485(+), 485(-), and ground must all be wired to the appropriate pins and will likely require a custom cable if you do not have access to screw terminal ports on the RedLion (because the pin-outs of the 9 pin connectors are not intended for use directly connecting to a 9 pin serial port on a PC/PLC).

The ASCII unit ID and the Modbus unit ID are separate things, and the device may show an ASCII unit ID of "A" but the Modbus ID is set to 1 by default.

As for the registers that you can read or write to, you may be able to get away with leaving off the 40000 (or in this case 400000) prefix and just entering something like 2053 or 2042 (as stated by in a prevuous comment). The Alicat Modbus RTU allows for only the two function codes to be called: function 03 for reading holding registers and function 16 for writing to multiple registers.

Additional info that may prove useful: When reading/writing to Alicat Modbus registers, the PLC should be indexed as base 1 to avoid reading and writing to the improper registers. I have also seen customers have issues if the data registers that use the two 16 bit registers are not decoded properly as a 32 bit float, so I would strongly second the recommendation to verify the temperature reading that was brought up in a previous post once you get it working.

If you would like to email me directly on the matter, I can be reached at [email protected]. Please let me know either through this forum or by email if you were able to get this up and running or if you have any questions, and I will do my best to assist.

Hello Kevin, thank you for the reply. When I observe the front panel of the MFC and to into "Misc2", scroll down twice, it displays "R65:Address 1". I would imagine that is the drop number for it, correct (unit number)?

I do not have it direct connected to a PLC. I have it connected to a RedLion HMI and am using Modbus RTU, and have set the AliCat as a slave to the RedLion. I am using pin 7 as +24VDC, pin 8 as VDC ground, pin 3 for my RS485-, and pin 5 as my 485+ (from DB9 connector), and then the +/- 485 from the RedLion are connected to the +/- of the AliCat.

I am not sure what "Function 3" and "Function 16" are.

 

[a062549]

I would not leave the Red Lion connected because establishing serial comm is always a *****.

There's lots of things that can trip up serial comm. If the Red Lion is connected, you have to figure out whether it is applying bias, whether it has termination built in, ya-da, ya-da.

I'd keep it as simple as possible, Modscan master on the PC with an RS-485 connection to the slave, the purpose being to prove that the slave communicates valid data from a given register.

The PC RS-485 connection can be either a USB/232 converter to a 232/485 converter or a USB/485 converter.

A bit late to the conversation, but fixed this one???

I'd make a cable and leave the pins out of the DB9 shell and bust out the MODSCAN. (Painful, but desperation often breeds insanity) In the two MODSCAN32 pics above the window implies you have not made a connection. as the "Number of polls:" indicates it has not polled yet.(?)
Let us know!

 

[danw]

In the two MODSCAN32 pics above the window implies you have not made a connection. as the "Number of polls:" indicates it has not polled yet.(?)

Modscan has not connected because it is not connected to anything. I posted the Modscan screen shots because the OP had not used a generic Modbus master to confirm communications.

I don't have the flowmeter device in question, in fact, I didn't have anything connected to Modscan, the screen shots are merely to show what elements need setup to get a reading.