INFICON RQCM - Quartz Crystal Microbalance Research System - Manual (Page 83)

RQCM – RESEARCH QUARTZ CRYSTAL MICROBALANCE
COMPUTER INTERFACE 7-7
31,255,109,53
This equals (31*256^3 + 255*256^2 + 109*256 + 53) = 536,833,333
To convert period to frequency, use the following formula:
Frequency (Hz) = (3.221E15)/Period = (3.221E15/536,833,333) = 6,000,000.0 Hz
Like sensor period, sensor resistance is also in special units. Use the following formula to
convert the resistance counts value sent by the RQCM to OHMs:
Sensor Resistance (OHMs) = (273,300/Counts) - 20
The scaling of the analog inputs depends on each inputs configuration as shown in the following
table.
Input Range Scaling (mV)
0 – 5 0.0001
+/- 5 0.0002
0 – 10 0.0002
+/- 10 0.0005
Example: To instruct the RQCM to output sensor #1 period and resistance, the computer would
send the following message:
Chr$(255)+Chr$(254)+Chr$(1)+Chr$(1)+Chr$(3)+Chr$(6)+Chr$(0)+Chr$(0)+Chr$(245
)
The RQCM will then send one message every 50 milliseconds that it 12 bytes long and
contains 6 bytes of data. The first four bytes of data is sensor period and the next two
bytes are sensor resistance.
Data logging is stopped by sending the following message:
Chr$(255)+Chr$(254)+Chr$(1)+Chr$(1)+Chr$(3)+Chr$(0)+Chr$(0)+Chr$(0)+Chr$(251
)
3. Configure Data Acquisition Board (Code #2)
This instruction allows the computer to configure the input range and temperature units of the
RQCM’s Analog Input/Temperature card. The following table shows the byte configuration for
this message.