Hired-Hand Farm Hand Series: Vent Master 24 - Manual (Page 33)

Part No. 4801-5124 rev 10-03 Farm Hand Vent Master 24 31
In addition, it can monitor the network to provide two other functions for emergency situations.
These other two functions do not have any effect on its primary job of monitoring the High and
Low limits. These functions are indicated with local network error codes (LN##). The
following shows the two error codes and explains how the Back-Up System functions during
these situations. These are very important functions to note because they can cause confusion
but they are important functions of the Back-Up System.
• LNE – Local Network Error
LNE indicates that the Back-Up System is unable to communicate with the Vent
Master 24. Therefore, the Back-Up System assumes that it is unable to communicate
with the SCS Relay Modules also. This triggers a very important function. The Back-
Up System will begin running its first stage of cooling (Cool1) on a back-up timer to
maintain minimum ventilation. It is also important to note that the Alarm Relay on the
Back-Up System will be triggered.
• LNO – Local Network Override
LNO indicates that the Back-Up System is communicating with the Vent Master 24 but
the Vent Master 24 is unable to communicate with 1 or more of the SCS Relay
Modules. This triggers the second important function. Since the Vent Master 24 is
unable to control the stages through its normal means. It will attempt to maintain the
environment through the Back-Up Systems output stages. Therefore, if the Vent
Master 24 is attempting to turn on Cool Negative stages over the local network but can
not, it will command the Back-Up System to turn on Cool1. Or, if the Vent Master 24
was trying to turn on a Heat stage it would command the Back-Up System to turn on
Heat. Refer to the SCS manual for a more detailed description of the Back-Up Systems
functions during the LNO condition. Again, it is important to note that this does not
impede the Back-Up System from doing its primary job of monitoring the temperature
against its High and Low Limits.
SCS-16 Relay Module and SCS-8 Expansion Relay Module
The SCS-16 and SCS-8 will be included in the same section because their error indicators are
identical. The function of these modules is to accept commands from the Vent Master 24 as
to which drive relays should be on. These devices communicate only with the Vent Master
24. They do not communicate with the Back-Up System. The Back-Up System is
connected to the relay cards on these modules through hard wiring. This is important to note
because the Back-Up System does not require the Local Net to be operating to override the
drive relays during an emergency back-up condition.
These modules contain LED indicators located in the top right hand corner of the board.
These indicators are tools to be used when trouble-shooting these modules. The following
list these indicators and explains there function.
• Power LED
This LED indicates that power is supplied to the board.
• Normal LED
This LED indicates the internal operation of the module. It is similar to the
LNE on the Back-Up System. It can indicate two functions as described
below:
1. On Continuously
In this condition, the module is receiving commands from the Vent
Master 24 and the data is determined to be correct.
2. Flashing
In this condition, the module is not receiving data from the Vent
Master 24 or the data is determined to be incorrect. At this time, the