KMAG4 - 260MHz Four-Sensor Magnetometer Counter
KMAG4 has several significant advantages to the other counters on the market - uses very high reference frequency (260MHz), delivers up to 1000 times per second at a good resolution, can sample only during specifyed time intervals (for example, only during the transmitter OFF time of a time domain EM system) and can be easily integrated in virtually every data acquisition system, because it is not designed to be part of a particular one. Each KMAG4 sample has a precise time tag.
Features
High Reference Frequency
R = B / (f * T), where
R - the resolution in pT
B - the magnetic field in nT
T - The sample time in ms
f - The reference frequency in MHz
As can be seen from the above formula, the absolute resolution depends on the reference frequency, magnetic field value and the sample time. The only one of those variables, depending on the counter design is the reference frequency - the higher the reference frequency, the better the resolution. The magnetic field value and the sample time should however be defined explicitly when specifying the absolute resolution. Otherwise, the numbers could be mislieading. It is not uncommon for a manufacturer to claim for example, that their counter has a resolution of 0.1pT without mentioning anything else. The number in such a case has most likely been calculated using the lowest magnetic field value (10000nT) and the longest sample time (1s), because this case provides the best number for the resolution. The higher reference frequency is the reason, KMAG4 provides so high resolution, compared to the other counters on the market, using 100MHz, 80MHz or 60MHz reference frequency. The higher reference frequency makes it possible to provide a good resolution even for shorter sampling times (more samples per second or sampling only during the off time of a time domain transmitter).
Below is a table that shows the KMAG4 - 260MHz counter resolution compared to the resolution of a 100MHz counter at different sample rates and different magnetic fields.
| Samples/sec | f[MHz] | B[nT] | ||
|---|---|---|---|---|
| 10,000 | 50,000 | 100,000 | ||
| 1 | 100 | 0.1 | 0.5 | 1 |
| 260 | 0.038 | 0.192 | 0.385 | |
| 10 | 100 | 1 | 5 | 10 |
| 260 | 0.385 | 1.92 | 3.85 | |
| 20 | 100 | 2 | 10 | 20 |
| 260 | 0.769 | 3.85 | 7.69 | |
| 50 | 100 | 5 | 25 | 50 |
| 260 | 1.92 | 9.62 | 19.2 | |
| 100 | 100 | 10 | 50 | 100 |
| 260 | 3.85 | 19.2 | 38.5 | |
As can be seen from the above table, KMAG4 provides better resolution than the 100MHz counters, even at twice the sampling rates. Even better - the table above shows that KMAG4 provides better resolution while sampling 50 times per second, than the 100 MHz counters sampling at only 20 times per second.
Common reference frequency for all four inputs
KMAG4 contains in fact four counters in the same box and can process the signals from up to four sensors. The four counters sample completely simultaneously and use the same reference frequency, providing exactly the same readings for all the four channels if the same signal is connected to them. The higher resolution, the same sampling time and the common reference frequency for the four counters make KMAG4 the perfect instrument for gradiometer applications.
Fast
The high reference frequency empowers KMAG4 to deliver up to 1000 samples per second at a good resolution
Precise and flexible synchronization with other equipment
The syncronization signal high level can be between +2.4V and +25V and its low level - between +0.6V and -25V. Any of the two synchronization signal edges can be specified to start a sample. The sample end can also be defined by one of the syncronization signal edges. The sample end can also be specified by defining the sample start delay and the sample time. The ability to take samples for a very short time (as short as 250 µs) and the very flexible synchronization modes make KMAG4 extremely convenient for applications like sampling during a time domain EM system transmitter OFF time for example.
Precize PPS Synchronization
KMAG4 uses a fast (50MHz) dedicated hardware circuitry to capture the active PPS signal edge and to provide the exact UTC Time of each sample if a GPS is connected. Thus its data can be synchronized with any other data having a time tag.
Easy Integration
- KMAG4 provides ASCII output records, consisting of data fields, separated by commas. Although the comma is the default field separator, any printable ASCII character can be configured for use as a field separator. The advantage of this output format is that the fields, not containing information during the current sample will be left empty. Thus the amount of information to be recorded will be reduced. Some data acquisition systems require every record to have a fixed number of characters however. KMAG4 can be configured to output a record with fixed number of characters in such a case.
- Can be easy configured to extract only the UTC time from the GGA string or to merge all the GPS data into its output string. Merging all the data into one string reduces the number of the RS232 ports, required by the data acquisition system.
- Becomes a magnetic base station if combined with SDAS data logger.
- Becomes airborne data acquisition system if combined with SDAS1-PPC (the Pocket PC Data Logger) and one (for up to 8 differential analog channels) or two (for up to 16 differential analog channels) KANA8 (the Eight-Channel Analog Module).
- Provides easy settings change through the serial port. Any communication program like Hyper Terminal can be used to type the necessary command to modify a setting. The modified settings are stored in a non-volatile memory.
Compact
The instrument is housed in an 6.8"W x 5.2" D x 2.2"H. aluminium box.
Front View
![[ KMAG4 Front View ]](images/kmag4-front_view.png)
ON
Power Supply LED
MAG1, MAG2, MAG3, MAG4
Two rows of BNC connectors. The bottom row is for the four sensors and the top one is for connecting an oscilloscope if necessary to observe the output signal of the associated sensor.
Rear View
![[ KMAG4 Rear View ]](images/kmag4-rear_view.png)
28VDC
A plastic circular four-pin power supply connector. KMAG4 itself will work if the power supply is between 12VDC and 32VDC. The actual power supply should meet the requirements of the sensors used. Pin 1 is connected to pin 3 and pin 2 - to pin 4 inside the box. Four 16AWG wires should be used for the power cable. The positive wires should be connected to pins 1 and 3 and the negative wires - to pins 2 and 4. Below is the list of the other parts, necessary to prepare the power cable:
| Item | Description | AMP Part # | Quantity |
|---|---|---|---|
| 1 | Plug Standard Sex | 206060-1 | 1 |
| 2 | Socket Contacts 18AWG-16AWG | 66181-1 | 4 |
| 3 | Cable Clamp | 1-206062-6 | 1 |
PORT1, PORT2, PORT3
Pin 9 of all three DB9 connectors are connected together through a hardware jumpers inside the box to provide an easy propagation of the PPS signal to other instruments.
- PORT1 is used to connect the GPS. Its Baud rate could be 4800, 9600, 19200, 38400, 57600, 115200, 128000, 230400, 256000, 460800, 576000 or 768000 bits/sec and it is configured as follows:
No parity; 8 data bits; No flow control
- PORT3 provides the output data. Its Baud rate could be 9600, 19200, 38400, 57600, 115200, 128000, 230400, 256000, 460800, 576000 or 768000 bits/sec and it is configured as follows:
No parity; 8 data bits; No flow control
- The PPS signal from the GPS can be connected to pin 9 of any of the three DB9 connectors.
- The synchronization signal, used in External Trigger Mode, can be connected to pin 1 of any of the three DB9 connectors.
Recommended Fuses
| Current Rating | Manufacturer | Part # |
|---|---|---|
| 2.5A | Littelfuse | 045203.5MR |