Geometrics, Inc. G-824A Magnetometer Manual
15
b.
Sample to sample noise less than 0.1 nT @ 10 Hz when not moving
6.
Larmor amplitude check and adjustment (Authorized Repair Facility only)
a.
Potentiometer on GSN board adjusted for 2.0 Volts Peak to Peak at
50,000 nT after 20 minute warm up
7.0 G-824A MAGNETOMETER
The CM-321 counter module is an integrated circuit that converts the cesium Larmor signal
(70 kHz to 350 kHz) into a numeric value indicating the magnetic field strength in
nanoTesla (20,000 nT to 100,000 nT in the earth’s field). In addition there are 8 each 12 bit
A/D channels where external or internal analog voltages can be digitized and appended to
the output serial data. This can be useful, for instance, in digitizing an analog altimeter
signal and incorporating it into the magnetometer data stream. A Julian clock string can be
enabled and added to the output data stream as well. There is an External Event pin that can
be used for external trigger or event marking. There is also an External Sync pin that can be
used to synchronize the magnetometer to timing devices such as GPS 1PPS (pulse per
second) regardless of the magnetometer sample rate.
In compliance with United States Government export restrictions, the G-824A does not
output the Larmor signal for external counting. Digitized Larmor is provided to the user
in RS-232 serial format from the G-824A serial port to a host computer (or Serial to USB
converter, see Keyspan.com) serial Com port. The RS-232 serial string configuration and
other features of the G-824A are configured by the user by choosing options from the G-
824A Configuration Menu. This menu is accessed via the host computer's Serial Com
port when connected to the RS-232 serial port on the G-824A.
Description
Weight
Dimensions
Cesium sensor package
P/N 27516-01
1lb. 8oz.
2’3/8”x5-1/2” cylindrical housing with 109 in. cable.
Termination: Burndy 0119 G6JF12-88 PNE
Electronics W/counter
P/N 27512-04
2lb. 5oz.
12-5/8” including connectors.
11-5/8” long x 2-1/2” cylindrical housing
Carrying Case
P/N 27615-01
10 lbs.
18l” x 9.5w” x 15h”
Analog signal cable
P/N 27565-02
14oz.
25’ coaxial with BNC termination
Digital signal/power cable
P/N 27611-02
2lb, 2oz.
25’ multi-conductor: Belden # 8418. Termination:
SP06A14-19S-SR and SP06A14-19P-SR
Power/data junction box
P/N 24870-20
9oz.
L 4-3/4”, W 3-1/4”, H 3-1/4”
Serial data cable
P/N 60-230-237
5oz.
6’, DB9
Optional AC/DC Power Supply
P/N 24810-02
2lbs.
(typical)
Input: 100VAC-240VAC @ 50-60 Hz; output 30VDC,
1.9A, 7” x 4” x 2.5” (typical) with 4’ output cord.
Table 3. G-824A standard component weights and dimensions
Table 4. G-824A interface cable pin-out
