Bacharach HGM300 Installation Manual - page 10
Communications LED Indicators
See Figure 4 for the locations of the communications LED indicators.
The communications adapter board has four LED communications status indicators
numbered 1-4. The meanings of these indicators are as follows:
LED 1 ON: Adapter is transmitting a poll/command to the HGM
LED 2 ON: Adapter is receiving a response from the HGM
LED 3 ON: Adapter is transmitting a response to Metasys N2
(because poll/command was directed to this slave)
LED 4 ON; Adapter is receiving a poll/command from Metasys N2
(directed to ANY N2 slave, not necessarily this one)
Under normal conditions, you would expect to see lots of activity on LED 4 since the N2
master is continually polling all N2 slaves on the line. LED 3 will show activity based on
how often the N2 master is polling the adapter (versus other N2 slaves on the line). If
there are few N2 slaves on the line, lots of polls will be directed to the adapter and LED 3
will blink frequently. If there are many N2 slaves, the adapter will be polled less
frequently and LED 3 will blink less frequently.
LED 1 and LED 2 will only show occasional activity. Since the refrigerant monitoring
process is fairly slow and new data is only available every 15 seconds or so, the adapter
polls the HGM at a slow rate to reduce the communications burden on the HGM main
processor.
Miscellaneous Notes
RS-485 communications wires ARE polarity sensitive. If the adapter does not
communicate on the N2 RS-485 port, try swapping the communications wires on the N+
and N- terminal block screws. The HGM port uses the same labels as the HGM main
board, so if you match the wires to the labels, polarity should not be an issue there.
If the adapter seems to not be functioning correctly, it can be restarted without restarting
the HGM simply by pressing the CPU RST button just below the “A” dipswitch. If you
restart the adapter by cycling the HGM’s power, you will have to wait for the HGM’s 15-
minute warmup cycle to end before PPM readings are available! If restarting the adapter
alone doesn’t help, then try cycling power to the entire HGM.
When the adapter software first starts, it attempts to establish communications with the
HGM before attempting to communicate on the N2 port. Do not be concerned after
cycling power or pressing CPU RST that no N2 activity is shown on the LEDs
immediately. The software delays about 20 seconds after a restart before attempting to
establish N2 communications.
The LEDs are driven by adapter software states, not by the RS-485 hardware. If an RS-
485 connection stops working in the middle of receiving a message, the RX LED may
stay on indefinitely until the connection starts working again.
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