42B Baratron Flow-through

Compact pressure switches
The 42B Flow-through 10 – 26,000 Torr Pressure Switch offers accurate and reliable protection for vacuum/pressure processes.

Designed for applications where a DC signal output is not required, these switches provide relay outputs that are readily interfaced with alarms, valve actuators, computers, process controllers, load locks and other protection devices. The 42B is referenced to atmospheric pressure. The trip point on can be set to trip above, below (reverse calibration), or exactly at current atmospheric pressure.

  • Flow-through configuration referenced to atmospheric pressure
  • Superb set point accuracy and low hysteresis
  • All-metal, all-welded construction exposing only stainless steel and Inconel for corrosion resistance
  • Switch relay can be set to energize above or below set point for fail-safe operation
  • High reliability reduces downtime

Baratron Capacitance Manometer Technology

Capacitance manometers are electro-mechanical gauges that can measure both pressure and vacuum. The capacitance gauge translates a pressure-modulated movement in a thin diaphragm into an electrical signal proportional to the pressure. The pressure sensor is the thin diaphragm that is exposed to the pressure or vacuum being measured via the inlet tube. An electrode is mounted in the reference cavity behind the diaphragm. Pressure differences between the process and the reference cavity deflect the diaphragm slightly, changing the distance between it and the electrode. Variations in this distance produce variations in the capacitance between the diaphragm and the electrode creating an electrical signal that is proportional to the pressure change. Since differences in the capacitance signal are produced by physical changes within the manometer and not by changes in the gas properties, pressure measurements by the capacitance manometer are independent of the composition of the gas being measured.

Referenced to Atmospheric Pressure

The 41B and 42B models are referenced to atmospheric pressure. The 41B/42B switches are often used to ensure a loadlock pressure has equilibrated to local atmospheric pressure before opening the door. The trip point on MKS’ atmospheric switches can be set to trip above, below (reverse calibration), or exactly at current atmospheric pressure.

Factory Set Trip Point

The relay trip point is factory set from 5% to 100% of the Full Scale pressure range. This means there is no need for personnel to adjust the set point and no safety concerns from an erroneously adjusted set point.

Fail-Safe Relay Operation

The relay mode on 41B, 42B, 51B, and 52B switches can be set to either energize above or below the set point. If the unit loses power, the relay switches to the Normally Closed position. The user can indicate whether the Normally Closed position is above or below the set point. Using Energize Above the set point as an example, the relay is in the Normally Open position when the pressure is higher than the trip point and Normally Closed when the pressure is below the trip point. The scenario is reversed for Energize Below the set point option. In vacuum systems, the fail-safe operation is if the system loses power causing the relay to de-energize, the relay is in the same state as the high pressure condition. Therefore, most vacuum systems require the relay energize with pressure decreasing or below the set point.

The 41B, 42B, 51B and 52B Vacuum and Atmospheric Pressure Switches provide increased accuracy over mechanical type switches, thereby providing tighter control and repeatability of process, improving throughput and yield.

KRISTIAN FLODSTRÖM Product specialist Vacuum technology 010-155 03 11