Chapter One: General Information
Introduction
17
Chapter One: General Information
Introduction
The MKS Type 1249A Solenoid Valve Driver positions a solenoid valve to achieve the desired
pressure in a system. The 1249 unit is designed to work with solenoid control valves such as the
MKS Type 148 and 248 valves, which are located upstream of the process. The small size of the
1249 unit enables it to fit into virtually any process control system.
The 1249 unit accepts an analog input signal as either a voltage (0 to 5 VDC or 0 to 10 VDC) or
a current (4 to 20 mA). Typically, the analog signal is sent from a computer or another device,
such as a programmable logic controller (PLC), equipped with a Proportional-Integral-Derivative
(PID) control algorithm. The external control device monitors the pressure of the system, using a
pressure transducer, and compares the pressure reading to a predetermined set point. The PID
control algorithm (in the PC or PLC) calculates the amount of valve control necessary to achieve
or maintain the process pressure at the set point value, and sends an analog signal, proportional to
the amount of change required to adjust the pressure of the process, to the 1249 unit. The 1249
module then controls the valve position accordingly.
The 1249 unit has a two digital inputs available on the Interface connector. The digital inputs
can use either TTL compatible logic or Open Collector control. The digital input signals
override the analog signal and position the valve in either the full open or full close position.
Note
The references to valve position (open or closed) relate to a normally
closed valve. The action will be reversed for a normally open valve.
If both digital inputs (OPEN and CLOSE) are activated, the CLOSE signal takes precedence and
the valve is fully closed. (For a normally open valve, the valve is fully opened.)
Protection from RF interference and noisy electrical environments is increased by the use of a
metal case, by internal design elements, and by the use of surge and ESD suppression networks
and RFI filtering on all inputs and outputs. The 1249 unit meets the testing standards required
for the European CE Mark when used with an overall metal braided shielded cable, properly
grounded at both ends.
The 1249 unit requires an external power supply of ±15 VDC ±5% @ 50 mA (excluding the
valve) or a +24 VDC ±5% @ 50 mA (excluding the valve).
