Lakeshore Learning Materials 642 - Manual (Page 113)

Lake Shore Model 642 Electromagnet Power Supply User’s Manual
Service 7-21
7.11.3.8 Calibrate External Current Programming Voltage Reading Gain
This procedure calibrates only the input voltage reading of the External Programming Input. The actual current output
from this input is specified to a 1% tolerance and is not adjustable. It is NOT necessary to engage the External
Programming feature of the Model 642 for this calibration.
1. Connect a new 9 V alkaline battery to the external current programming input lines (positive to positive input).
2. Send “CALG 7, 1”. To set the external programming voltage reading gain constant to 1.
3. Get the Model 642 external programming voltage reading and record (V
reading
).
NOTE: To get this reading from the Model 642, press and hold the Status key on the front panel until the display
goes dark (~3 seconds). When the key is then released, a diagnostics display will be seen. The upper right
reading, “Ext Prog”, is the reading needed for this step.
4. Measure the voltage directly across the 9 V battery and record (V
measured
)
5. Calculate the gain constant per the following equation:
Programming Voltage Reading Gain Constant = V
measured
/V
reading
6. Verify the gain constant to be 1, ±0.05.
7. Send “CALG 7, constant”.
8. Verify the Model 642 external programming voltage reading to match the measured 9 V battery voltage within,
±0.0005 V.
9. Send “CALSAVE” to write this calibration to non-volatile memory.
7.11.4 Calibration-Specific Interface Commands
The following interface commands are only used during calibration and are in addition to those listed in Chapter 5.
CALG Gain Calibration Constant Command
Input: CALG <type>, <value>[term]
Format: nn, ±nnnnnnn
<input> Specifies the item to calibrate. Valid entries are:
0 = Output I Reading
1 = Bias A Reading *
2 = Bias B Reading *
3 = Gnd Diff Reading *
4 = Out Con Reading *
5 = Output V Reading
6 = Boost V Reading*
7 = Ext Prog Input Reading
8 = Temp Reading*
9 = Out Stg V Reading *
10 = Actual Output Current
<value> Gain calibration constant value.
Remarks:
Items marked with a * are for internal diagnostic use only and should always be set
to a value of 1 (default).