Connecting to a single instrument

# Import the propar module
import propar

# Connect to the local instrument, when no settings provided
# defaults to locally connected instrument (address=0x80, baudrate=38400)
el_flow = propar.instrument('COM1')

# The setpoint and measure parameters are available
# as properties, for ease of use.
el_flow.setpoint = 16000
el_flow.setpoint = 0

# All parameters can be read using the process and parameter numbers,
# as well as the parameters data type.
el_flow.read(1, 1, propar.PP_TYPE_INT16)

# Most parameters can also be read by their FlowDDE number,
# for example the user tag parameter.
el_flow.writeParameter(115, "Hello World!")

Connecting to an instrument with multiple channels

Some instruments are a single node (one address) but contain multiple channels (for multiple sensors). To connect to a specific channel, specify the channel when creating an instrument instance. If no channel is specified the first channel will be used.

# Import the propar module
import propar

# Connect to an instrument by specifying the channel number to connect to
flow = propar.instrument('COM1', channel=1)
pressure = propar.instrument('COM1', channel=2)

# Alternatively, pass channel to parameter functions
instrument = propar.instrument('COM1')
p_upstream = instrument.readParameter(205, channel=2)

Connecting to multiple instruments

When instruments are connected to a FLOW-BUS network, the localhost function an instrument can be used to connect to other instruments on the network (by specifying the node address).

# Import the propar module
import propar

# Connect to an instrument by specifying the instrument node address to connect to
el_flow = propar.instrument('COM1', 3)
cori_flow = propar.instrument('COM1', 4)
es_flow   = propar.instrument('COM1', 5)

Custom baudrate

It is also possible to connect to an instrument with a different baudrate than the default of 38400 baud. Note that it is only possible to connect using the baudrate that is configured in the instrument.

# Import the propar module
import propar

# Connect to the local instrument, with a different baudrate than the default (38400)
el_flow = propar.instrument('COM1', baudrate=115200)

Scanning for instruments

To check all connected instruments on the network, the propar modules master can be used. When creating an instrument on a specific com port, a propar master is automatically created for that comport. Using the get_nodes function of the master, a list of all nodes on the network is collected and returned. This list can be used to check if all expected instruments are connected, or to get an overview of your network.

The nodes list will also include the number of channels that are present on that device. Use this in combination with the channel functionality to create instances of each device and for the seperate device channels.

# Import the propar module
import propar

# Connect to the local instrument.
el_flow = propar.instrument('COM1')

# Use the get_nodes function of the master of the instrument to get a list of instruments on the network
nodes = el_flow.master.get_nodes()

# Display the list of nodes
for node in nodes:

Using a master

It is also possible to only create a master. This removes some abstraction offered by the instrument class, such as the setpoint and measure properties, the readParameter and writeParameter functions, and having to supply the node number on each read/write parameter call.

# Import the propar module
import propar

# Create the master
master = propar.master('COM1', 38400)

# Get nodes on the network
nodes = master.get_nodes()

# Read the usertag of all nodes
for node in nodes:
  user_tag = master.read(node['address'], 113, 6, propar.PP_TYPE_STRING)


Finally the propar module offers the possibility of using the chaining mechanism of the propar protocol to read or write multiple parameters using a single propar message. This is advanced functionality and has some downsides, especially when it comes to error handling. As the read_parameters and write_parameters functions do not return True or False to indicate success, but instead rely on the underlying propar status codes to indicate the result of the action.

# Import the propar module
import propar

# Connect to the local instrument.
el_flow = propar.instrument('COM1')

# Prepare a list of parameters for a chained read containing:
# fmeasure, fsetpoint, temperature, valve output
params = [{'proc_nr':  33, 'parm_nr': 0, 'parm_type': propar.PP_TYPE_FLOAT},
          {'proc_nr':  33, 'parm_nr': 3, 'parm_type': propar.PP_TYPE_FLOAT},
          {'proc_nr':  33, 'parm_nr': 7, 'parm_type': propar.PP_TYPE_FLOAT},
          {'proc_nr': 114, 'parm_nr': 1, 'parm_type': propar.PP_TYPE_INT32}]

# Note that this uses the read_parameters function.
values = el_flow.read_parameters(params)

# Display the values returned by the read_parameters function. A single 'value' includes
# the original fields of the parameters supplied to the request, with the data stored in
# the value['data'] field.
for value in values:

# For writes the parameter must have the 'data' field set with the value to write when
# passing it to the write_parameters function.
params = [{'proc_nr': 1, 'parm_nr': 1, 'parm_type': propar.PP_TYPE_INT16, 'data': 32000}]

# Write parameters returns a propar status code.
status = el_flow.write_parameters(params)

# Also, note that when using the master directly the address of the node must be set in the
# parameter object that is passed to the read_parameters or write_parameters function
params = [{'node': 3, 'proc_nr': 1, 'parm_nr': 1, 'parm_type': propar.PP_TYPE_INT16}]

# Read from the master directly
values = el_flow.master.read_parameters(params)


To easily generate a list of parameters for use with chaining, and the read_parameters and write_parameters functions, the propar database can be used. This component is automatically available on all instrument instances or can be instantiated separately.

# Import the propar module
import propar

# Create a database instance
db = propar.database()

# or access the instruments database instance
el_flow = propar.instrument('COM1')
db      = el_flow.db

# Get parameter objects for chained read (read_parameters) from list of FlowDDE numbers
parameters = db.get_parameters([8, 9, 11, 142])

# Get a single parameter object
setpoint = db.get_parameter(8)

# It is also possible to search the database, using the string name of the parameter
valve_parameters = db.get_parameters_like('valve')

Custom serial class

To use a custom serial data provider (instead of pySerial), the serial_class can be passed to the instrument and master classes.

# Import the propar module
import propar

# A dummy serial port class with the required functions and attributes.
class dummy_serial():

  def __init__(self, port, baudrate, **kwargs):
    # Initialize the port, port and baudrate can be controlled
    # in instrument and master initialization.
    print(port, baudrate)

  def close(self):
    # Close the port

  def open(self):
    # Open the port

  def read(self, size=1):
    # Read data from port, return bytes object
    return b'dummy'

  def write(self, data):
    # Write data to port, bytes object as input

  def in_waiting(self):
    # Return number of bytes available for reading
    return 5

# Instrument instance with dummy serial port.
dut = propar.instrument('dummy_port', serial_class=dummy_serial)