HP 34970A Alarm Limits, Transducers and Sensors

Chapter 3 System Overview

Data Acquisition System Overview

Transducers and Sensors

Transducers and sensors convert a physical quantity into an electrical quantity. The electrical quantity is measured and the result is then converted to engineering units. For example, when measuring a thermocouple, the instrument measures a dc voltage and mathematically converts it to a corresponding temperature in °C, °F, or K.

Measurement	Typical Transducer Types	Typical Transducer Output
Temperature	Thermocouple	0 mV to 80 mV
	RTD	2-wire or 4-wire resistance
		from 5Ω to 500Ω
	Thermistor	2-wire resistance from
		10Ω to 1 MΩ
Pressure	Solid State	±10 Vdc
Flow	Rotary Type	4 mA to 20 mA
	Thermal Type
Strain	Resistive Elements	4-wire resistance from
		10Ω to 10 kΩ
Events	Limit Switches	0V or 5V Pulse Train
	Optical Counters
	Rotary Encoder
Digital	System Status	TTL Levels

Alarm Limits

The HP 34970A has four alarm outputs which you can configure to alert you when a reading exceeds specified limits on a channel during a scan. You can assign a high limit, a low limit, or both to any configured channel in the scan list. You can assign multiple channels to any of the four available alarms (numbered 1 through 4). For example, you can configure the instrument to generate an alarm on Alarm 1 when a limit is exceeded on any of channels 103, 205, or 320.

You can also assign alarms to channels on the multifunction module. For example, you can generate an alarm when a specific bit pattern or bit pattern change is detected on a digital input channel or when a specific count is reached on a totalizer channel. With the multifunction module, the channels do not have to be part of the scan list to generate an alarm.

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