Series 900 Single & Dual Instruction Manual

The alarms are a normally, open collector transistor outputs; that is, a transistor is used as a switch to ground. A “High” alarm means that if the flow signal is higher than the alarm trip setting, the transistor will be turned on. Conversely, a “Low” alarm activates the transistor when the flow signal is lower than the alarm trip setting. Sierra products usually incorporate a means of configuring the output as either a high alarm or low alarm. System Boxes contain both.

It is necessary to limit the current flow through the transistor to 100 mA maximum. The Standoff Voltage is set at 30 VDC. This means that the transistor can safely withstand 30 VDC on it’s collector while in the off state. Voltages greater than this may cause failure of the transistor. (See Section 3.4 for specific instructhe alarm levels.)

Following are several examples of commonly used alarm circuits:

APPENDIX D

Alarms for System Electronics

Relay Interface

 

 

Optional External

 

 

 

 

Power Supply

 

 

 

 

+15

 

 

 

 

PS

+15

+15

 

NO

 

 

 

 

100mA

NC

 

 

COM

 

MAX

 

 

 

 

 

 

 

°

 

 

 

 

Alarm

 

 

 

 

Out

 

 

 

 

 

Alarm “on” actuates relay

“Window” Alarm

High

Alarm output: LED Alarm will light if either high

or low alarm is acti- vated to indicate flow is outside preset high and low limits.

Low

Alarm

+15

1K

 

 

 

LED

 

 

Simple Indicator Light

+15

1K

LED

Note: See IM for Back Panel

Connection & Pin Numbers.

Isolated Open Collector Output

+15

MOC8020

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Sierra Not available instruction manual Appendix D, Window Alarm