
HPQ2-IP SP101009.102 – 10 October 2012
MKS Instruments, Spectra Products
18
3.8 Reset Switch
The reset switch is accessible through a hole in the rear panel and is labelled
RESET.
Pressing the switch performs a hardware reset on the microprocessor in the
HPQ2-IP control unit.
3.9 External Trip
The external trip connector is a 3.5mm Jack socket mounted to the right of the
Power connector on the rear panel and labelled
X-TRIP.
The external trip feature is used to protect the filaments from exposure to high
pressures. It allows an independent total pressure gauge or a signal from a vacuum
control system to be connected to the HPQ2-IP. It is the most effective of the trips
available and we would always recommend its use. The external trip input can be
driven in three ways.
1. Uncommitted relay contact
This is a low voltage (+5V, 1mA) contact. The contact should be closed for normal
operation, open to trip the filaments or if the protective equipment is switched off.
2. Open collector TTL drive
The output transistor should be on for normal operation, open for trip or if the
protective equipment is turned off.
3. Totem pole TTL drive
The signal should be low for normal operation, high for a trip condition or if the
protective equipment is switched off.
The external trip circuitry is fully isolated from the system ground.