Perma Pure Mini-GASS 2812T - Manual (Page 35)

Control system safety interlock –
The interlock system is present to provide an output signal that can be used internally to
stop sample flow via the sample isolation valve or optional internal sample pump. This
system can also be used to provide an external output to a PLC or other
control/monitoring system so that the status of the Mini-GASS can be monitored.
Two relays are used to perform this function –
• Low purge flow relay - A differential pressure switch across the purge air ports of
the PD dryer senses the flow of purge air and energizes this relay when flow is
present. A minimum purge flow rate of about 10 lpm is required. Below this flow,
the alarm relay will de-energize.
• Low temperature relay – The CAL 3300 temperature controller has an alarm
function that is used to energize this relay when the system is operating at
normal temperature. The actual point at which a low temperature alarm is
triggered is Set-point minus 5C. For instance, if the temperature controller is set
at 90C, the alarm relay will de-energize at 85C.
The interlock system is used in the Mini-GASS to control the sample gas isolation valve
or optional internal sample pump by simply supplying power to the interlock valve coil or
sample pump motor via the alarm relays. Each of the relays is of a DPDT or double pole
double throw design. This just means that there are two sets of normally open/normally
closed (N.O./N.C.) contacts in each relay. One set of contacts is used internally and one
set of contacts is provided to allow connection to an external system.
• Refer the drawing MG-1228-04-12. Internally these relays are wired in series to
supply power to the sample isolation valve or sample pump. To accomplish this,
switched line voltage (115,230VAC, Orange wire) is supplied to the common
(term. #5)connection of the low purge flow relay. From the normally open (term.
3) connection of the low purge flow relay, a brown wire connects to the common
(term. 3) connection of the low temperature relay. From the normally open (term.
3) connection of the low temperature relay, a gray wire connects to the sample
isolation valve or sample pump. This allows the valve to open or the pump to
start only if both relays are energized.
• Refer to the graphic to the right. For external
connection, the second set of contacts in each
relay is “dry”. No power is applied. This allows the
user to determine the control voltage that will be
used. A typical use of the alarm signals is, as
described above, to control sample flow. The actual
use is left up to the customer.