Teledyne 4220 installation and operation guide Submerged Probe

	4220 Flow Meter
	Section 1 Introduction
1.3.1 Submerged Probe	The submerged probe is mounted beneath the surface of the flow
Operation	stream and measures liquid level by responding to changes in
	hydrostatic pressure against the probe's sensing element. The
	probe contains an IC (integrated circuit) differential pressure
	transducer. This transducer provides an output signal that
	changes proportionally to the pressure placed against it by the
	flow stream. The 4220 converts this signal to the flow rate with
	level-to-flow rate conversion formulas or tables characteristic of
	the primary device at the site.

1.3.2Transducer Operation The transducer in the submerged probe detects pressure with a small stainless steel diaphragm that transfers pressure to a silicon diaphragm containing a resistance bridge. Pressure against one side of this diaphragm causes it to flex slightly. This flexing causes the resistors on one side of the bridge to stretch, while the resistors on the other side of the bridge compress. The result is an unbalance in the current across the bridge, that is proportional to the increase of hydrostatic pressure caused by an increasing level in the flow stream. This bridge is fed from a con- stant-voltage source, so any change in its output is a result of hydrostatic pressure against the transducer.

CAUTION

You may need to disassemble the submerged probe for clean- ing. If you do, do not touch the metal diaphragm inside the probe with either your fingers or tools. Deforming the dia- phragm even slightly may ruin the transducer. Flush the dia- phragm with gently running water only.

The inner face of the transducer disk is referenced to the atmo- sphere through the internal vent tube that runs the full length of the probe’s cable. The outer face is subjected to the pressure exerted by both the flow stream and the atmosphere. The dif- ference between the two pressures exerted on the diaphragm is the hydrostatic pressure.

CAUTION

Any obstruction in the reference port of the cable could cause faulty level readings. Moisture in the reference port can lead to permanent internal damage to the probe. Keep the reference port free of debris and moisture.

The output from the transducer is low and the impedance is high, so an in-line amplifier boosts the signal to make sure the flow meter can still detect it even when the submerged probe and the flow meter are separated by some distance. The amplifier is encapsulated in the box mounted on the submerged probe cable near the connector.

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