ModBus and USB Serial Terminal Instructions for Thermal Flow Meters

Tactical Flow Meter ModBus and USB Serial Terminal Command Instructions for Thermal Flow Meters.

Revision Date: Update: May 10, 2018 to add Youtube Embed code and functional links.


The Tactical Flow Meter uses the Modbus RTU Communication protocol. To enjoy the highest level of resolution many values are transmitted as CDAB Longs, that by default, according to the ModBus RTU protocol. These CDAB Longs carry a 10,000 multiplier to provide FOUR digits of precision. To parse the reading from the flow meter the user need only divide the returned Long CDAB value by 10,000.  We also provide some variables in the CDAB Float that are in the IEEE 752 format. These are used in emulation modes for various manufacturers.

Factory Tactical Flow Meter ModBus COM Setup:

BAUD 19200
Data Bits: 8
Parity: Even
Stop Bits: 1
Termination Character: NONE

ModBus Register List:

Note: Zero Suppression provides the user with the ability to suppress readings from the flow meter, however we will not suppress the Sensor RAW value from your being able to read it. The suppression is handy for suppressing low value totalizing events and low end control system anomalies.

Configuration Registers:

These registers are from one single sample and are for reference.

ModBus Super Simple Program:

You may wish to skip getting ModBus Pro in favor of using the simnple program shown above. It is very simple and is only provided as a test tool to assist you in using the ModBus protocol and learning how to parse out the data. The Tactical Flow Meter has constants in the form of an I32 Integer, a IEEE 754 Single Float from 4 bytes and a string.

Download Link here 

Watch Video below to see how to use the program.


Configuration Software:

Website link for Configuration Software.

Android App:

Website Link for Android App. This program is specifically designed for the Tactical Flow Meter.

Serial Terminal:

Download Link for Serial Terminal.  This program is a very simple, and small footprint, Serial Terminal to communicate to the Tactical Flow Meter using the USB port. You will be directed to the page that looks like the image below. Right click and download and install on your PC. There is a SINGLE Executable so there is no messing with your Registry!

The Image from Parallax download site is below:

Once downloaded, unzip the file (NOTE… You must UNZIP and NOT run the executable from the Windows UNZIP viewer function) and put the Parallax-Serial-Terminal executable in an easy to find location.

We suggest putting it here: C:\TacticalFlow

Once the Parallax Serial Terminal is running select the COM port for the Tactical Flow Meter.

You may wish to invoke the Windows Device Manager to find which COM port Windows has assigned, or enumerated, to the Tactical Flow Meter by typing Device Manager in WIndows Start Icon as shown below:

Then, click the Device Manager that shows up above:

In this example, my serial port is COM3. To CONFIRM which COM port your Tactical Flow Meter is using simply unplug and plug the USB cable and you will see  that Windows re-enumerates the serial ports and the one you see appear and dissappear is the COM for the Tactical Flow Meter.

Start the Parallax-Serial-Terminal and configure it like THIS if your COM is COM3:

Then click Enable   and to test your connection type 43 to view the revision of the meter.

Your Serial Terminal dashboard should look like this:

VERY IMPORTANT NOTE for using the ANY Serial Terminal: 
You will be communicating using an ASCII protocol to provide for simple verification and configuration using a Serial Terminal. As such, to read the value of the registers you ADD ONE to the command set below.

For example, Mass Flow Units is Command 20 in ModBus but for the ASCII Serial Port the command to READ the Mass Flow Units is 21. If you accidently issue 20 or some EVEN number, justchange the 20 to 201. In any serial terminal you do NOT get to edit what you enter, there is no backspace recognized. You just hit ENTER and start again. Just make sure to never type an EVEN number in any Serial Terminal. If you DO mess up your meter you can always RECOVER the Factory Values as shown here at 12:48 on the time line.

If you wish to view EVERY CONFIGURATION Register in your meter, and save it for study, then issue 94,99 and hit enter. Below is an example of the registers, or commands, for each variable stored in a typical Tactical Flow Meter. 

The Short List above has the following:

See the LONG list below.. Notice the #20 corresponds to the same as Command 20 above..

The complete list of Command Registers is shown below:

EVEN numbers are WRITES and ODD numbers are READS. To READ the Mass Flow Units, Command 20, you will issue 21 in the Parallax Serial Terminal.

Modbus Poll:

Website link for Modbus Poll. This program is one of the more commonly utilized debugging tools for folks who use Modbus. It carries a free 30 day trial period to allow usert to debug Modbus enabled installations

Modbus Poll Website Link for Free Download for 30 days

ModBus Poll configuration examples

Simple Modbus Poll user Instructions to read Slave ID 48, on COM 10, Engineering Flow, Register 106:

  1. Start Modbus Poll
  2. Connect Tactical Flow Meter to the RS-485 connections via the three connections of RS-485 GND, RS-485- RDB +, and RS-485 RDA -. If you see no control it could be likely you will only have to swap the RS-485- RDB + and RS-485 RDA -. Wires because not all companies label the terminals the same way.
  3. Use Device Manager to identify the COM port your USB to RS-485 converter. In this example we see we are on COM 10.
  4. On ModbusPoll hit File/New.. Yields the following screen. There are many ways to START Modbus Poll but this way is simple and makes it easy to understand. 
  5. Setup/Read Write Definition as shown, click APPLY and then OK, We are READING a holding register with this method.: 
  6. Connect the COM port to the Flow Meter. Hit Connection/Connect (or F3) and fill out as below, hit OK: 
  7. Highlight the two registers as shown below, We are telling Modbus Poll we want to apply the Display settings, coming up, to these two registers.: 
  8. Click Display and using the select as shown above we have as follows, This allows Modbus Poll to display the register we are reading according to the format of the register in the Tactical Flow Meter.: 
  9. The reading shows the flow rate of 9.1689 in this example after you widen the field 

ModBus Poll Serial COM Setup:

Examples with ModBus Poll

ModBus Poll to read Flow Units, Register 20:

ModBus Poll to read Totalizer, Register 218:

The totalizer is a LONG in the form of CDAB that gains the resolution by storing the total flow using a 10,000 scaling factor to yield four digits of resolution.

Link to Online version of this document in Google Docs.

HEX Converter Example for Tactical Flow Meter Floats

VERY NICE Online HEX Converter here See example image below...

HEX Conversion example for Tactical Flow Meter Float