Table of Contents
Advertisement
3.2.6
DIFFERENTIAL MEASUREMENT MODE
RPM4-AD can be set to operate in differential measurement mode. Differential measurement
mode is used to measure airspeed and varying altitude (see Section 3.2.3).
In differential measurement mode, the measured pressure is the difference between
measurements of the two Q-RPTs (Hi – Lo, Pt – Ps).
To set up differential measurement mode, use [RANGE] (see Section 3.3.1) to select the
<Hi> Q-RPT or the <airspeed & altitude> shortcut. If the shortcut is not used, once the
Q-RPT has been selected, use [MODE] (see Section 3.3.3) to set absolute and differential
measurement mode.
3.2.7
AUTOZERO FUNCTION
RPM-AD includes an AutoZero function. This function is used to rezero the Q-RPT readings
in gauge and differential modes and to offset the Q-RPT relative to a reference standard in
absolute mode.
See Section 3.5.1 for complete information on the AutoZ function.
In gauge measurement mode, AutoZ should be run when the mode is first selected and any
time RPM4-AD is vented (zero gauge pressure applied) (see Section 3.3.9.1).
In differential measurement mode, the AutoZ function should be run when the mode is first
selected and any time zero differential is set or the line pressure (altitude) is changed (see
Section 3.3.9.3).
In absolute measurement mode, it is recommended that AutoZ be run every 30 days or
when RPM4-AD has been exposed to temperature changes exceeding 15 ºC (36 ºF) (see
Section 3.3.9.2).
3.2.8
SDS SELF DEFENSE SYSTEM
The RPM4-AD Q-RPTs modules 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 module's TEST port
and opened to the module's VENT port (See Section 5.6, Figure 8, Figure 9).
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 and TEST ports, 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-AD can be operated as if SDS were not installed (see
Section 3.5.4.2).
SDS is normally used to isolate an RPM4-AD Q-RPT from a test system which may
sometimes be subjected to pressures higher than the Q-RPT's 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-AD 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. This is not a fail safe overpressure system. It does
not protect against very rapid overpressure or pressure exceeding 10 MPa (1 500 psi).
See Section 5.6 for schematics of the RPM4-AD Q-RPTs and pneumatic system and
indication of internal valve states for SDS open and closed.
Page 21
© 2005-2007 DH Instruments, a Fluke Company
3. OPERATION
Advertisement
Table of Contents
