How to Use Modbus/TCP Modules as Remote I/O with Honeywell Trendview Recorders – 8400641
Honeywell Trendview Recorder & Acromag 967EN Modbus/TCP Module as Remote I/O
The Acromag 967EN has 8 analog 4-20mA inputs. It’s a Modbus/TCP slave, making it ideal for; use as remote I/O, with a Honeywell paperless Trendview recorder that runs as a Modbus/TCP master, over a standard Ethernet network connection.
The Acromag 967EN provides data in either floating point or signed integer formats.
Signed integers values range 1 to 20,000 counts across the 4-20mA input span; so scaling to user friendly engineering units has to be done on the recorder. Floating point values can be scaled to engineering units in the Acromag and read directly as scaled values. If the scaling in the Acromag is correct, then no scaling is needed in the recorder’s pen math.
Acromag setup is done via web browser, thus no software is needed. Typical input and scaling setup changes made in the web browser are downloaded and executed quickly; on the order of seconds. No ON-OFF power cycles are required for input configuration changes.
Acromag’s sample time is 8mS; so the Acromag data tends to be noisier than the same signal wired into a recorder. The solution: let the 967EN average multiple samples. Start with 20 as a number to average with.
The 200 ohm 4-20mA analog input resistance will not unduly load a loop-powered circuit. However, it will inhibit HART communications (HART requires 230 ohms, minimum).
Acromag’s i2o remote messaging function writes values only to other Acromag products. Hence, i2o is not applicable for use with Trendview.
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