ALPHA TDR-5000
General:
The TDR-5000 is developed for the measurement of the Dielectric Constant of fluids or bulk goods. A two inch parallel wire sensor picks up the measure value. It is connected to the main unit via a 2 meters BNC coaxial cable. The measure result is available in nearly real time. So it is possible to observe and automatically regulate dynamic processes. Unlike gauges with capacitive measuring the TDR-5000 also can handle middle-grade conductive (up to 1mS/cm) materials. For example, measurements lead to the same results with distilled water (isolating) or with mineral water (conductive).
Applications:
- Investigation of Waste Water
- Moisture of soil measurements
- Motor oil control
- Gas content of soil measurements
- Ecological Technologie
Functional Description:
The TDR (Time Domain Reflection) principle is dependent upon a time measurement. The TDR-5000 periodically sends voltage pulses with very short rise times (250 ps) onto the sensor cable. Let us have a look at one single pulse`s way: The pulse runs along the coaxial cable up to the point t1, that's the connection point of the parallel wire sensor. At this point the electrical impedance of the conductance changes, therefor a part of the impulse's energy is reflected and runs back on the cable. The rest of energy runs towards the end of the sensor wires (point t2), where another part of the energy is reflected, running back to the source (TDR-5000). There a special sampling circuit analyses the time delay of the partly reflected pulse energy, eliminating the constant run time of the cable. The found sensor run times are shown on a display and are available as a DC-Voltage value. The paragraph following describes how the dielectric properties of the observed material can be found from the measured sensor run time.
Dielectric Constant K
In free space (K=1) the expansion speed of electromagnetic waves is equal to expansion speed of light. It is decreased with raising Dielectric Number K. For poor loss, non magnetic materials there is approximately:
v = Electromagnetic expansion speed, c = light expansion speed, K = Dielectric Constant of the medium the expansion is happening in. By TDR-5000 displayed run time t across the sensor (t = t2 - t1), put into the following relation leads to the value of K:
l = length of the sensor sticks.
Example:
Length of sensor l = 5 cm, t = 3 ns measured. Result: K = 81 (water).
Calibrating of Range:
1. Method:
- By connecting the delivered Calibration Cables instead of the Sensor the range of time can be calibrated as follows (linear time scale):
- 1.) Connect BNC-Cable 2m. Set "RANGE" to left (counterclockwise) position.
- 2.) Turn "POSITION" until "0" is displayed.
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3.) Connect one of the Calibrating Cables to the BNC-Cable 2m. Turn "Range" clockwise until 10,00 (full range) is displayed. Repeat steps 2) and 3).
Now the range is calibrated to full display level. E.g.: 5ns/10V respectively 0.5 ns/V. -
4.) Connect the Sensor. Set display by "POSITION" to 0.33 ns. According to 0.66 V/1.66 V/6.66 V for ranges 5 ns/2 ns/0.5 ns per 10 V.
If l = 5 cm and K = 1 (air) the run time t is 0.33 ns (see calibration).
2. Method:
- By immersion of the Sensor into mediums of well known dielectric constants as p.e. Air (K=1), Ethanol (K=26) or Water (K=81), "Position" and "Range" calibration is very easy (Logarythmic K-Scale).
Advices:
The sensor rods need to be dipped completely.
Specification:
- Sensor: Two sticks from 1 … 3 mm-wire, min. length 40 mm, distance 5 … 10 mm, Connection via BNC-Cable 50/75 Ohm (RG58/RG59) , length 2 m. Isolated cutoff (mounting range) 10 mm max. Parallel not critical.
- Isolation: The sensor sticks are allowed to be isolated by a thin coating.
- Range: Controlable from about 0,3 to 5 ns (Nanoseconds) by RANGE-knob. Measuring window moveable by "POSITION"-knob. Linear time scale. A magnifing effect is available by "Range" and "Position".
- Resolution: The achievable resolution is given by the sampling rate and by the physical noise of the electronic components.
- As a time value is measured, we declare the basic noise in the time range as: Äquivalent noise-time: < 5 ps rms, broadbandnoise.
- Lowpass-filter: If there is enough measuring time, the resolution could be raised by using an extern lowpass-filter.
- Display: Digital Display with 3 1/2 digits 0.00 to 10.00 V
- DC out: DC voltage 0 … 10 Volt via BNC-connector
- Settle time: < 10ms (identical with Alpha LM 1-S)
- Power supply: 115/230 V AC 4,5 VA
Accessory:
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Handheld sensor 5 cm with 2 m BNC-Cabel
BNC extension cable 2 m
BNC calibration cable 0.5 ns
BNC calibration cable 2 ns
BNC calibration cable 5 ns
Sensors for your special utilization could easily be made by yourself or by us:
