NAME

INTRODUCTION

spec communicates with the Amptek MCA-8000 and MCA-8000A pocket MCA devices over an RS-232C interface. The serial communication is nonstandard and requires spec to set the DTR and RTS modem-control outputs and read the DSR and CTS modem-control inputs. Thus spec only supports this MCA on platforms with serial ports that respond to the standard modem-control ioctl() calls. The MCA can be used with baud rates up to 115200, although maximum effective transfer rates seem to be about half that.

The pocket MCA can collect data in up to 16,384 active channels, although it has memory for 32,768 channels. Memory group sizes can be configured from 256 to 16,384 channels in powers of two, and the number of groups is 32,768 divided by the group size.

The number of usable channels is reduced slightly, though, due to "the sliding scale linearization technique" employed by the pocket MCA ADC. The number of channels in a group is reduced by 1/32 of the group size. For a 256-channel group, the last 8 channels are not useful. For a 16,384-channel group, the last 512 channels are not useful. spec fills those locations with zeroes.

The pocket MCA can be powered by either batteries or an external power source. The power can be turned on remotely by sending a special sequence of signals over the DTR and RTS modem control lines. When spec starts up or on a "reconfig" command, spec sends the signals that will turn on the pocket MCA if had been turned off. When operating on battery, the pocket MCA turns itself off after two minutes of inactivity. While the MCA is acquiring data, spec will normally poll the MCA to check its status, which will keep the MCA from shutting off. If the MCA does shut itself off, spec will send the signals to turn the MCA back on and then retry the command.

FUNCTIONS

The standard MCA commands supported by spec are described in the mca help file. Of the standard functions, the Amptek pocket MCA supports mca_get() (but not mca_put()). The standard mca_par() options "info", "chans", "max_chans", "max_channels", "disable", "auto_run", "soft_preset", "auto_clear", "native_type", "preset", "live", "real", "elapsed_live", "elapsed_real", "dead", "run", "halt", "clear", "group_size", "select_group", "gain" and "chan#", are supported by the Amptek pocket MCA.

The options, "group_size" and "gain" are synonyms as are "max_chans" and "max_channels".

Legal values for the "group_size" argument are 256, 512, 1024, 2048, 4096, 8192 and 16384. Legal values for the "select_group" argument are from 0 to (32768/group_size) - 1.

The native data type for the MCA is ulong, i.e.,  unsigned long (32-bit) integers.

The "auto_clear" mode is on by default. Note, however, it takes time (proportional to the group size) to clear the data. Thus, count times not using a preset will be affected.

Additional mca_par() options are as follows:

mca_par("show_status")

Reads and displays the current parameters from the MCA status word.

mca_par("time_stamp")

Reads the time stamp of the current data group and returns a value in UNIX time format (the number of seconds since the start of Jan 1, 1970). The ASCII representation is available as: date(mca_par("time_stamp")).

mca_par("time_stamp", value)

Updates the time stamp to match the time passed in UNIX time format via value. If value is zero, the current system time is used.

mca_par("threshold")

Reads the pocket MCA status and returns the current threshold value.

mca_par("threshold", value)

Sets the pocket MCA threshold to value. The threshold is the channel number of the lowest channel to be used for data collection. Channels below the threshold channel don't collect data.

mca_par("battery_type")

Returns the state of the battery-type flag in the pocket MCA. The battery type is used to calculate the remaining battery power. Battery type zero is 1.5 Volt alkaline cells. Battery type one is for 1.2 Volt NiCad cells.

mca_par("battery_type", value)

Sets the battery-type flag in the pocket MCA. A value of zero selects 1.5 Volt alkaline cells. A nonzero value selects 1.2 Volt NiCad cells. The battery type is only used for choosing which scale to use to calculate the remaining battery capacity.

mca_par("battery")

Returns the remaining battery capacity as a percentage based on the battery type and the battery value returned in the pocket MCA status word.

If the magnitude of the counts is known to be less then 65536 in each channel, the read-out time can be cut in half by only reading the two low-order bytes for each data point. spec implements a "read_short" mode to implement the faster read. Note, the native data type remains ulong.

mca_par("read_short")

Returns nonzero if "read_short" mode is on, otherwise returns zero.

mca_par("read_short", value)

Sets "read_short" mode to on or off according to whether value is nonzero or zero.