ATECo PTS-1 Pressure Time Switch for Purging Aircraft Ground Support Test Equipment

Figure 1 ATECo PTS-1 Pressure-Time Switch

                                Figure 2 EK-217 B Test Box

Shown at left is the completed assembly of the pressure-time switch designed for the EK-217B test boxes (above) that is used for development test and production calibration for the AS-907/HTF-7000 fuel controls. The timer and power relay circuit is designed onto a printed circuit board that fits inside the Dwyer 1950-00 pressure switch housing as shown below.

Figure 3  Cross Section Illustration of PC Board Installation

To illustrate construction overview, Fig 3 shows a cross section of the Dwyer pressure switch identifying the spacers and how the circuit board mounts on the MicroSwitch.

The PC board and its components are shown in Green and the spacer nuts are blue. The original relay’s 3-hole SPDT contact pinout was modified by drilling two holes in the PC board to fit the 4-hole DPDT contact configuration. Two jumpers were added on the PC board to connect the DPDT contacts in parallel to use both sets. The new power relay physically fits inside the pressure switch housing and still meets the electrical requirements.

The following construction details show pictures of the switch, explain the modification and installation of the timer circuit board.

Figure 4 Dwyer 1950 Switch with Cover Off

Figure 5 Inside of pressure switch with Microswitch shield machined down.

The modification is to cut the nylon shield down flush, to slightly below the top of the microswitch. On the left side of the switch is the 3W resistor used to drop voltage down from 110VAC to 24VAC before rectifying and filtering to power the timer circuit.

Figure 6 Top View of Circuit Board

Figure 7, Bottom View of Circuit Board

This is the timer circuit board that fits inside the 1950 pressure switch enclosure. The rectangular hole in the center fits over the raised portion in the center of the micro switch. The Timer circuit is located at the top, and a 10A 225VAC electromechanical relay is located on the back side at the bottom. The bottom view at right shows the 10A 250VAC relay.

Fig. 8 shows the completed pressure-time PC Board installed in the Dwyer 1950 pressure switch enclosure. This package saves money, weight and room inside of the test box.


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