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RPM4™ OPERATION AND MAINTENANCE MANUAL
© 2004-2007 DH Instruments, a Fluke Company Page 24
3.2.7 SDS SELF DEFENSE SYSTEM
Q-RPT modules designated 7M or lower that are NOT liquid filled are equipped with the SDS self
defense system. The SDS system includes hardware and embedded software to isolate Q-RPTs
from overpressure. When SDS is CLOSED for a Q-RPT module, the Q-RPT is isolated from the
modules TEST(+) port and opened to the modules VENT port (See Section 5.6, Figure 8).
SDS can be OPENED and CLOSED from the front panel using [SDS]. SDS can also be
controlled using functions under [SPECIAL], <4SDS>. The SDS “temp open/close” function
allows SDS on both Q-RPTs, whether active or inactive, to be opened and closed directly
(see Section 3.5.4.1). The SDS “full time on/off” function allows SDS to be opened permanently
so the RPM4 can be operated as if SDS were not installed (see Section 3.5.4.2).
SDS is normally used to isolate an RPM4 Q-RPT from a test system which may sometimes
be subjected to pressures higher than the Q-RPTs maximum pressure. When configuring a
multi-range system, this can eliminate the need for external valving or connecting and
disconnecting RPM4s. For example, two Q-RPTs of different ranges might be connected to
a single calibration system. When the Hi Q-RPT is in use, SDS is closed on the Lo Q-RPT to
protect it from overpressure. When used in this manner, SDS should be CLOSED prior to
applying pressure. Automatic SDS closing in response to overpressure should only be used in
an emergency overpressure situation.
SDS also attempts to protect Q-RPTs from accidental overpressure. Whenever RPM4 is
powered ON it continuously monitors the pressure read by its Q-RPT(s). If the pressure
reaches the maximum pressure limit for a Q-RPT, SDS CLOSES to isolate the Q-RPT from
the TEST port and vent it to atmosphere (see Section 3.4.4.1). This is not a fail safe
overpressure system. It does not protect against very rapid overpressure or pressure
exceeding 10 MPa (1 500 psi).
When an RPM4 is used as an external device to a PPC3 pressure controller, PPC3 controls the
RPM4’s SDS to isolate the RPM4 Q-RPTs from the test pressure when they are not in use.
IF the RPM4 SDS is “full time off” PPC3 changes it to “ON”.
The maximum pressure that should be applied to an RPM4 TEST(+) port when SDS is
CLOSED is 10 MPa (1 500 psi).
Though the SDS self defense system includes features to automatically protect Q-RPTs
against accidental overpressure, SDS should NOT be considered a fail-safe overpressure
protection system. SDS cannot guarantee that overpressure damage will NOT occur.
Conventional measures for overpressure protection should also always be used. Damage
to Q-RPTs due to overpressure is NOT covered by the RPM4 product warranty even when
SDS is present and ON.