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For the 0-5 V output signal, the externally connected load must have an impedance of <br /> more than 200 kilo-ohms. For the 4- 20 mA output signal,the externally connected load <br /> must have an impedance of less than 200 ohms when powering the personalDataRAM <br /> with a battery, or less than 300 ohms when using the its AC supply. <br /> Since both voltage and current outputs are present at the same time,both can be used <br /> concurrently,if so required. <br /> The accuracy of the analog output signals is better than 1% of the reading with respect <br /> to the digital reading. <br /> 11.0 ALARM <br /> 11.1 Alarm Description and Operation <br /> The personalDataRAM alarm function is provided both as an audible signal as well <br /> as an electrical output.The audible alarm consists of a series of beeps generated by <br /> an on-board piezo-transducer.The electrical output, available at the digital <br /> communications port, consists of a 1 Hz square wave signal which can be used to <br /> trigger/activate other equipment through an appropriate interface (consult with the <br /> factory). <br /> The alarm function can be enabled/disabled by the user through the <br /> personalDataRAM keyboard (see Section 8.2). Setting of the alarm level must be <br /> performed on the PC (see Section 9.0). <br /> The alarm is triggered whenever the preset alarm level is exceeded based either on : <br /> a) the displayed real-time concentration,if ALARM:INSTANT was selected (see <br /> Section 8.2), or b) a 15-minute running average concentration,if ALARM: STEL was <br /> selected.When the concentration falls below that level the alarm condition stops. <br /> While the alarm is on the user can stop it(i.e. silence the alarm)by pressing any key <br /> of the personalDataRAM. If the concentration continues to exceed the set alarm level <br /> after 10 seconds,however, the alarm restarts. <br /> 11.2 Alarm Output <br /> A pulsed voltage output is available on the personalDataRAM in synchronism with <br /> the audible signal.This signal consists of a 1 Hz square wave with an amplitude of <br /> 5 V pp. An externally connected load should have an impedance of no less than 100 <br /> kilo-ohms.This alarm output signal is available at pins 2 and 5 (counting from top <br /> to bottom) of the 6-contact output/communications port on the side of the <br /> personalDataRAM (see Figure 5 or 6). <br /> 11.3 Remote Alarm Unit <br /> An alarm relay unit(MIE model pDR-RA) is available as an optional accessory for <br /> the personalDataRAM. The pDR-RA,when connected to the alarm output of the <br /> 27 <br />