cal radar instrumentation has grown to include a myriad

of sensors and trans-

mitters. Today, radar

serves us in applica-

tions that range from

the commonplace to

the cosmic. Radar

maps the topology

of distant planets

and pinpoints

weather fronts on

earth (doppler

radar); it automati-

cally opens supermarket doors (continuous wave

radar); and it cooks our meals with microwaves (cavity

magnetron radar). Radar is presently the fastest growing

measurement technology for industrial level control.

But radar’s beginnings were less than auspicious.

Early level instruments were costly, bulky, over-special-

ized and complicated. The development of simpler, less

costly and easier-to-use devices would be made possible

by solid state components and by a growing fund of

applications knowledge.

position of process liquids by measuring the interval

between the emission and return of high frequency

radio waves. Guided Wave Radar, used by Magnetrol’s

Eclipse

that launches its signal along a waveguide that runs

directly into the process media. Pulse Burst Radar, uti-

lized by Pulsar

technology that launches its signal into open air along a

trajectory directed toward the process media.

gies commonly used for radar, Magnetrol products

employ a pulse burst approach rather than frequency

modulated continuous wave (FMCW). Pulse Burst Radar

operates in the time domain and does not require

complex and expensive processing as needed to

enable FMCW. Because echoes are discrete and

separated in time, Pulse Burst Radar is better

able to sort through extraneous echoes and

select the one generated by true level. Pulse Burst

Radar also has excellent averaging characteristics,

important in those applications where a return signal

is attenuated by the factors described below.

Unlike true pulse devices that transmit a single,

sharp (fast rise-time) waveform of wide-band energy,

Magnetrol products emit short bursts of 5.8/6.3 GHz

(Pulsar) or 26 GHz (Model R82) energy and measures

the transit time of the signal reflected from the liquid

surface. Distance is calculated utilizing the equation:

Distance = C

× Transit time (C = speed of light)

2

The Level value is then developed by factoring in Tank

Height and Sensor Offset information. The exact refer-

ence point for distance and level calculations is the

Sensor Reference Point—bottom of an NPT thread, top

of a BSP thread, or face of a flange.

Equivalent Time Sampling (ETS) measures the high

speed, low power electromagnetic energy (EM). ETS is

critical in the application of radar to vessel level meas-

urement. The high-speed EM energy is difficult to meas-

ure over short distances and at the resolution required

in the process industry. ETS captures the EM signals in

real time (nanoseconds) and reconstructs them in

equivalent time (milliseconds), which is much easier to

measure with today’s technology.

ETS is accomplished by scanning the waveguide to

collect thousands of samples. The round trip event on a

65 foot (20 meter) tank takes only 133 nanoseconds in

real time. After it is reconstructed in equivalent time it

measures 200 milliseconds.

by three basic conditions: (1) the

Dielectric of the

process medium; (2) the

Distance, or measuring range

3

1 ns

500 ns