DH Instruments PPCH, PPCH-G, 401875 Instruction Sheet

Replacing PPCH and PPCH-G

Valve Driver Board

INTRODUCTION

In August, 2006 the PPCH and PPCH-G valve driver board
p/n 401875 was revised to replace the mechanical relays on
it with a solid state circuit. The mechanical relays have
been found to occasionally not switch when they should,
causing misoperation of the valve. PPCHs with serial
number lower than 238 and PPCH-G lower than 245 are
likely to have been delivered with the old board.

The difference between the old board and revised board is
easily identified by the part number imprinted on the board
(which is the bare board part number). The old board is p/n
123630; the revised board is p/n 123630 Rev. B.

It is recommended that the old board be replaced with the
revised board for all PPCH and PPCH-G pressure
controller/calibrators in the field.

P/N 401875

Instruction Sheet

Figure 2. Control valve module cover plate

Figure 1. Valve driver board

To replace the valve driver board, proceed as follows:

Turn unit off and remove power. Disconnect rear panel

pressure connections.

Access the PPCH or PPCH-G mechanical module by

opening the fasteners on the rear panel and sliding out
the module (see Section 5.9 of the PPCH Operation
and Maintenance Manual).

Document 560084 060907

DH Instruments, Inc.

4765 East Beautiful Lane
Phoenix AZ 85044-5318
USA

Figure 3. Valve driver board installed

Remove the (6) 2.5 mm socket head bolts that hold the

control valve cover plate.

Lift off the cover plate carefully and disconnect the

servo driver cable from the valve driver board.

Disconnect the stepper motor and micro switch

connections from the valve driver board.

Remove the four 2.5mm sockethead cap bolts that hold

the valve driver board to the chassis and remove the
board. Note the orientation of the board.

To install the new board, follow step to in reverse

order.

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