Yes. However, it may depend on modems and software being used. Acromag participated in a joint venture and “cross-country” application test with Hach Company. Hach Company initiated a 25 hour dial-up test from Colorado to Michigan. The setup and results are below:
PC: Dell Dimension L433C, 433Mhz Pentium PC with 128Meg of Ram and Windows 2000 Pro SR1.
Host Modem (Colorado location): SixNet VT Modem 2 (self dialing modem) with firmware version 1.06. Settings were 9600 baud fixed, no parity, 8 data bits, enable self dialing, enable continuous connection, 12 self dial retry count, 2 min retry delay, ignore DTR, disable echo and disable error correction.
Remote Modem (Michigan location): SixNet VT Modem 2. Settings were 9600 baud fixed rate, 1 stop bit, and no parity. It was configured to answer after 1 ring.
Remote Location Modbus I/O: Two Analog modules (Model 917MB AO-I’s and Model 913MB AI-I’s) were connected to the RS485 side of the remote modem. The 4 channels of AO on the 917MB were also looped/wired to the 4 channels of the AI terminals on the 913MB for a "loop-back" test. The communication settings for both modules were: 9600bps, 8 data bits, no-parity, 1 stop bit, 1 start bit, and Modbus-RTU communications. The address for the 913MB and 917MB was addresses 1 and 247, respectively.
Software: The Hach Process Link OPC Server, version 1.0. The OPC Server Settings were poll rate = 30 seconds, time out = 5000 milliseconds, baurd rate = 9600, and retry count = 5. The Hach Data Logger OPC Client, version 2.0 logged the data to a CSV file at 1 minute intervals. The tags logged were the 4 Analog Input and 4 Analog Output Values from the modules. The datatype in the OPC datalogger was set to Integer (4byte) for the display of the 917MB AO values.
Test Results Summary (after 25 hours of testing):
1. No loss of logged data at the one-minute interval in the Hach Datalogger CSV file
2. The Hach Process Link OPC Server reported 31175 messages sent and 30838 messages received, 337 time outs, and 0 read and write errors
3. The 913MB module stats in the OPC Server were:
a. Read Message Count 22623
b. Read Message fail count 231
c. Read message retry count 231
d. % read message success 98.9796
4. The 917MB module stats in the OPC Server were:
a. Read message count 8846
b. Read message fail count 120
c. Read message retry count 119
d. % read message success 98.6444
5. A typical Process Link Event Log Error is:
a. Addr: F7 Failed read, error code: 11 Modbus Exception, code:00
Conclusion: Successful communications over long distance was maintained for 25 hours. The read message rates have a success rate greater than 98 percent with polling rates faster than 30 seconds and logging rates at 1 minute or longer. No data was missed in the log.