PD940 DIPSTICK

The PD 940 Dipstick is a hygienic electronic level, conductivity and temperature sensor for electrically conductive liquids in a metal tank. A special flange welded onto the tank provides for easy clamp mounting of the Dipstick.

The Dipstick has a hygienic and robust design suitable for food industry and performs very fast measurements making it ideal for inline process control.

Level measurement is independent of conductivity and works with different liquids without any calibration.
Foam on top of liquids, like in a milk air eliminator, contributes to level with the equivalent liquid content in the foam.
Level output is measured in meters starting from the isolation between the tip and stick.

Conductivity measurement is level independent and is factory calibrated with a cell constant that fits most applications. It is useful to detect water, milk or CIP liquids in the tank without further calibration.
For precise conductivity measurement, it is possible to adjust the cell constant according to the actual tank diameter or to conductivity measured with a reference instrument.
The module also includes an analog source output (4-20 mA) and a Digital I/O that can source 1 A to ground.
The Dipstick is programmable in COPP, which means that part of or all of an automation application can run in the Dipstick. The program can make use of ready-made components to control and monitor any process or machine application, locally in the Dipstick as well as via the network, interacting with other devices.

Measurement principles:
• The isolated tip part measures resistance to tank.
It is converted to conductance and scaled with the cell constant to show specific conductivity for the liquid
• The stick part measures resistance to tank. Level is calculated as the ratio between stick and tip resistance scaled with the tip length.
• The accurate Pt1000 sensor in the tip use a speed up algorithm to calculate the final tip temperature in advance.

Accurate and reliable measurement conditions:
• The tip is always completely covered with liquid
• Measurements assume constant vertical tank area (e.g. a cylinder)
• Liquid conductance is within specified limits for the module
• Tank, stick and tip is clean and without isolating layers
• Distance from stick and tip to tank is more than 50 mm

Note that the conductivity of liquids are temperature dependent.
For absolute conductivity measurement, the cell constant must fit the tank diameter.

Typical conductivity examples
Fresh cow milk: 4-5 mS/cm
Tap water: 0.005 to 0.5 mS/cm (soft to hard water)
CIP liquid: 100 mS/cm (water with 2% NaOH or HNO3)

Different measurement situations with and without foam

Without foam
1. Valid liquid level and conductivity.
2. Valid zero liquid level and conductivity.
3. Invalid zero liquid level. Conductivity out of range.
Tip must be covered by liquid.

With foam
4. Valid equivalent liquid level of foam and conductivity.
5. Valid equivalent liquid level of foam and conductivity.
6. Invalid foam level.
Zero level if foam conductivity is out of range.
Tip must be covered by liquid.

Digital Output (source)
Oneshot and Dutycycle time resolution: 417 µs
Internal resistance: Typ. 0.5 Ω
Output start current (duration max 200 ms): Typ. 5 A
Load current at ON (Source only): Max. 0.5 A
Short circuit cutoff delay time (current > 5A): 104 µs
Leak current at OFF: Max. 500 µA

Temperature Measurement
Process temperature range: 0-100 °C
Calibration error: @ 20 °C +/-0.6 °C
Resolution: 0,1 °C
Update frequency: 200 ms

Power Specifications
Supply voltage: nominal 24 VDC
Supply voltage: 12 – 32 VDC
Typ. internal power consumption: (@ 24 VDC) 0.5 W

Environmental Conditions
Operation temperature: -25 °C to +70 °C
Storage temperature: -40 °C to +85 °C
Protection class: IP67

Mechanical Specifications
Weight approx (lenght 500 mm): 1600 g
Vibration: IEC 60068-2-6 : 2007

Mechanical Specifications
Weight approx (lenght 500 mm): 1600 g
Vibration: IEC 60068-2-6 : 2007

Tank part