Databases

quadEM.template

The quadEM.template database provides control of the electrometer using the standard asyn device support. NDPluginStats from ADCore provides digitally averaged readings of the current, sum, difference and position with user-defined averaging time. It also provides the standard deviation, minimum, maximum, and other statistics, including a histogram of array values.

drvInfo string

EPICS record name

EPICS record type

asyn interface

Access

Models supported

Description

QE_MODEL

$(P)$(R)Model

mbbi

asynInt32

r/o

All

The model of the electrometer. This is normally determined automatically by the driver by reading the firmware version. It can also be specified in the configuration command. Values are:

  • 0: Unknown

  • 1: AH401B

  • 2: AH401D

  • 3: AH501

  • 4: AH501BE

  • 5: AH501C

  • 6: AH501D

  • 7: TetrAMM

  • 8: NSLS_EM

  • 9: NSLS2_EM

  • 10: NSLS2_IC

  • 11: PCR4

  • 12: SoftDevice

  • 13: T4U

QE_FIRMWARE

$(P)$(R)Firmware

waveform

asynOctet

r/o

All

The firmware version of the electrometer. In R6-0 this was changed from a stringin record to a waveform record of length 256 because the TetrAMM firmware string is longer than 40 characters.

QE_ACQUIRE_MODE

$(P)$(R)AcquireMode, $(P)$(R)AcquireMode_RBV

bo, bi

asynInt32

r/w

All

Acquire mode. Values are:

  • 0: “Continuous” Acquires data continuously until Acquire is set back to 0.

  • 1: “Multiple” Acquires NumAcquire acquisitions and then automatically stops acquisition, setting Acquire back to 0.

  • 2: “Single” Acquires a single acquisition. This is a convenience, it is identical to Multiple with NumAcquire=1.

Multiple and Single mode are typically used for data acquisition.

QE_ACQUIRE

$(P)$(R)Acquire

busy

asynInt32

r/w

All

Acquire command. This command turns acquisition from the device on (1) and off (0) Since it is a “busy” record the device can be used for step-scanning with the sscan record when AcquireMode=Single.
Important note: Operation in Single mode with the sscan record also requires that the statistics plugins be set to have CallbacksBlock=Yes so that the driver waits for the statistics plugins to compute before it sets Acquire back to 0.

QE_READ_FORMAT

$(P)$(R)ReadFormat, $(P)$(R)ReadFormat_RBV

bo, bi

asynInt32

r/w

All except NSLS_EM, NSLS2_EM, and PCR4

Read format from the device. Values are:

  • 0: Binary

  • 1: ASCII

In binary mode the AH401 and AH501 send integer data with no delimiters or terminators. This can lead to problems if the data stream is somehow corrupted because there is no way to know where one set of readings end and the next set begins. This should not happen under normal conditions because the devices use TCP, which guarantees retransmission of dropped packets. However, it has been observed to occur. In binary mode the TetrAMM sends IEEE 754 double-precision values for each channel, followed by a Signalling NaN. The NaN is thus effectively a terminator that can be used to synchronize the data stream if it is somehow corrupted. ASCII mode is robust against the synchronization problem, since each reading ends with terminator characters. However, ASCII mode is generally slower. On the AH401 ASCII mode appears to be able to do 500 reading/s, which is sufficient except for the case when IntegrationTime=.001 and PingPong=Yes. On the AH501 ASCII mode ranges from 7 to 10 times slower than binary mode. On the TetrAMM ASCII mode requires a minimum value of ValuesPerRead of 500, which limits the update rate to 200 Hz. In binary mode the minimum value of ValuesPerRead is 5, which is an update date of 20 kHz, or 100 times faster than ASCII mode.

QE_RANGE

$(P)$(R)Range, $(P)$(R)Range_RBV

mbbo, mbbi

asynInt32

r/w

All

Range command. This selects the sensitivity of the electrometer (A/D units per nanoamp).
For the TetrAMM the choices are:

  • ±120uA

  • ±120nA

For the AH501 series the choices are:

  • ±2.5mA

  • ±2.5uA

  • ±2.5nA

For the AH401 series this selects the feedback capacitor, which controls the gain of the device. There are 8 capacitor choices in units of saturation charge:

  • 1800 pC

  • 350 pC

  • 300 pC

  • 250 pC

  • 200 pC

  • 150 pC

  • 100 pC

  • 50 pC

For the NSLS_EM this selects the feedback capacitor, which controls the gain of the device. There are 8 capacitor choices in units of saturation charge:

  • 350 pC

  • 300 pC

  • 250 pC

  • 200 pC

  • 150 pC

  • 100 pC

  • 50 pC

  • 12 pC

For the NSLS2_EM this there are 5 ranges:

  • 1 uA

  • 10 uA

  • 100 uA

  • 1000 uA

  • 5000 uA

For the PCR4 v1 there is 1 range:

  • 50 uA

For the PCR4 v2 there are 4 ranges:

  • 50 mA

  • 250 uA

  • 2.5 uA

  • 25 nA

QE_PING_PONG

$(P)$(R)PingPong, $(P)$(R)PingPong_RBV

mbbo, mbbi

asynInt32

r/w

AH401 series, NSLS_EM

The AH401 series, and the NSLS_EM have 2 input channels, which we call Ping and Pong here. This doubles the speed of the unit, because one channel is being digitized while the other is integrating. This record selects how the two channels are treated.
On the AH401 series the choices are “Off” (0) and “On” (1). “Off” only returns the data from the Ping channel. This reduces noise because only a single integration capacitor is used, but it reduces the data rate by a factor of two, because data are only returned on every other integration time. “On” returns the data from both channels, which doubles the data rate at some expense in noise.
On the NSLS_EM the choices are “Phase0” (0), “Phase1” (1), and “Both (2). “Phase0” only returns the data from the Phase0 channel, Phase1 from the Phase1 channel, and Both from both Phase0 and Phase1. The device can only return Phase0 and Phase1 correctly when ValuesPerRead=1. The driver automatically sets PingPong=Both if ValuesPerRead is not 1.

QE_INTEGRATION_TIME

$(P)$(R)IntegrationTime, $(P)$(R)IntegrationTime_RBV

ao, ai

asynFloat64

r/w

AH401 series, NSLS_EM

Selects the integration time of the amplifier. As the integration time is increased the sensitivity increases, but the number of readings/sec sent from the device is decreased.
For the AH401 series values range from 0.001s to 1.000s. The data are sent after one integration time if PingPong=”On” or after 2 integration times if PingPong=”Off”.
For the NSLS_EM the values range from .0004s to 1.0 s. Both the Phase0 (Ping) and Phase1 (Pong) values are sent at after a time period equal to IntegrationTime * ValuesPerRead.

QE_NUM_CHANNELS

$(P)$(R)NumChannels, $(P)$(R)NumChannels_RBV

mbbo, mbbi

asynInt32

r/w

TetrAMM and AH501 series

Selects the number of channels to measure and transmit data for. Using fewer than 4 channels increases the sampling rate. Allowed choices are:

  • 1: channel 1 only

  • 2: channels 1 and 2 only

  • 4: channels 1-4

QE_GEOMETRY

$(P)$(R)Geometry, $(P)$(R)Geometry_RBV

mbbo, mbbi

asynInt32

r/w

All

Selects the geometry of the current inputs as discussed above. Allowed choices are:

  • 0: Diamond

  • 1: Square

QE_RESOLUTION

$(P)$(R)Resolution, $(P)$(R)Resolution_RBV

mbbo, mbbi

asynInt32

r/w

AH501 series

Selects the resolution of the ADC in bits. Using 16-bits increases the sampling rate by a factor of 2 relative to 24-bits. Allowed choices are:

  • 16: 16-bit data

  • 24: 24-bit data

QE_BIAS_STATE

$(P)$(R)BiasState, $(P)$(R)BiasState_RBV

bo, bi

asynInt32

r/w

TetrAMM, AH501C, AH501D, and PCR4

Selects the state of the bias supply output voltage. Allowed choices are:

  • 0: Off

  • 1: On

QE_HVS_READBACK

$(P)$(R)HVSReadback

bi

asynInt32

r/o

TetrAMM

Readback of the actual status of the bias supply output. Possible values are:

  • 0: Off

  • 1: On

This will stay On for a few seconds after setting BiasState to Off, while the voltage is ramped down to 0.

QE_BIAS_INTERLOCK

$(P)$(R)BiasInterlock, $(P)$(R)BiasInterlock_RBV

bo, bi

asynInt32

r/w

TetrAMM

Selects the state of the bias supply interlock. Allowed choices are:

  • 0: Off

  • 1: On

QE_BIAS_VOLTAGE

$(P)$(R)BiasVoltage, $(P)$(R)BiasVoltage_RBV

ao, ai

asynFloat64

r/w

TetrAMM, AH501C, AH501D, NSLS2_EM, and PCR4

Controls the voltage of the bias supply output.

QE_HVV_READBACK

$(P)$(R)HVVReadback

ai

asynFloat64

r/o

TetrAMM

Readback of the actual voltage of the bias supply output.

QE_HVI_READBACK

$(P)$(R)HVIReadback

ai

asynFloat64

r/o

TetrAMM

Readback of the actual current in microamps of the bias supply output.

QE_VALUES_PER_READ

$(P)$(R)ValuesPerRead, $(P)$(R)ValuesPerRead_RBV

longout, longin

asynInt32

r/w

All

On the TetrAMM this record controls the number of readings that are averaged in the TetrAMM using the NRSAMP command. The TetrAMM always digitizes at 100 kHz (10 microseconds per sample). The minimum value of NRSAMP (and hence ValuesPerRead) in Binary mode is 5, which means the maximum number of values per second is 20000. Setting ValuesPerRead to 100, for example, will average 100 readings in the TetrAMM, and thus result in a 1000 values per second sent from the TetrAMM to EPICS.
On the NSLS_EM and NSLS2_EM this record controls the number of readings that are summed in the hardware., For all other models ValuesPerRead controls the number of values that are read from the meter in a single call. These values are averaged in the driver before it does any callbacks. The default is 1 (no averaging).
Increasing ValuesPerRead will reduce the CPU time because:

  • On the TetrAMM it reduces the number of readings per second sent, from the maximum of 20000, to 100000/ValuesPerRead.

  • On the NSLS_EM it reduces the number of readings per second sent, from the maximum of 2500 (depending on IntegrationTime, to a maximum of 2500/ValuesPerRead.

  • On the NSLS2_EM it reduces the number of readings per second sent, from the maximum of 10000 (depending on internal setting of ADC rate)to 10000/ValuesPerRead.

  • On the AH401 and AH501 series the driver reduces the frequency of asynOctet->read() calls by a factor of ValuesPerRead, because it can obtain multiple readings from the meter in a single call. This is particularly significant on the AH501 series, which can transmit up to 26,040 readings per second.

  • It reduces the frequency of callbacks to device support.

The potential disadvantages of larger values for ValuesPerRead are:

  • It will change the statistics computed by the NDPluginStats plugin because an initial averaging operation has already been performed, which reduces the standard

  • deviation, changes the histogram, etc.

  • On the NSLS_EM it prevents selecting only Phase0 or Phase1 with the PingPong record.

  • It will reduce the sampling frequency of the TimeSeries support

  • It will reduce the update frequency of the EPID fast feedback support.

QE_SAMPLE_TIME

$(P)$(R)SampleTime_RBV

ai

asynFloat64

r/o

All

Provides the actual time between sample readings from the device. This is controlled by the following parameters:

  • ValuesPerRead: All models

  • IntegrationTime: AH401 series, NSLS_EM

  • PingPong: AH401 series and NSLS_EM

  • NumChannels: AH501 series

  • Resolution: AH501 series

The sample time on the TetrAMM is controlled by the following equation:

  • 10 microseconds * ValuesPerRead.

The sample time on the AH501 series is controlled by the following algorithm:

  • SampleTime = 38.4 microseconds * NumChannels * ValuesPerRead

If Resolution == 24 then SampleTime = SampleTime * 2
The minimum sample time (NumChannels=1, ValuesPerRead=1, Resolution=16) is 38.4 microseconds, or a sampling frequency of 26.04 kHz. The maximum sample time with ValuesPerRead=1, NumChannels=4, Resolution=24 is 307.2 microseconds, or a sampling frequency of 3.255 kHz. Setting ValuesPerRead > 1 will increase the sample time and reduce the sampling frequency proportionally.
The sample time on the AH401 series is controlled by the following algorithm:

  • SampleTime = IntegrationTime * ValuesPerRead

If PingPong == 0 then SampleTime = SampleTime * 2
The minimum sample time is 0.001 seconds, or 1 kHz sampling frequency. The maximum sampling time (PingPong=0) is 2 seconds, or 0.5 Hz sampling frequency. Setting ValuesPerRead > 1 will increase the sample time and reduce the sampling frequency proportionally., , The sample time on the NSLS_EM is controlled by the following algorithm:

  • SampleTime = IntegrationTime * ValuesPerRead

If PingPong != Both then SampleTime = SampleTime * 2
The minimum sample time is 0.00041 seconds, or 2.5 kHz sampling frequency. The maximum sampling time (PingPong!=Both) is 2 seconds, or 0.5 Hz sampling frequency. Setting ValuesPerRead > 1 will increase the sample time and reduce the sampling frequency proportionally.

QE_AVERAGING_TIME

$(P)$(R)AveragingTime, $(P)$(R)AveragingTime_RBV

ao, ai

asynFloat64

r/w

All

Controls the time period over which values are accumulated in the ring buffer before they are read out into NDArray objects and any registered plugins are called. AveragingTime is actually used to compute NumAverage_RBV=AveragingTime/SampleTime_RBV. The callbacks are done when the number of values in the ring buffer equals NumAverage_RBV, and exactly NumAverage_RBV values will be passed to the plugins.
However, setting AveragingTime=0 will set NumAverage_RBV=0 as well, and will disable automatic callbacks to areaDetector plugins. In this case data will only be read from the ring buffer when the ReadData record is processed. This will read out all available data from ring buffer, and the actual number of values read will be NumAveraged_RBV. This mode could be useful when the quadEM is being used for data acquisition, for example in a scan. In this case processing the ReadData record will read all values that have accumulated in the ring buffer since ReadData was last processed. ReadData must be processed frequently enough to avoid ring-buffer overflow.
On the TetrAMM in External Bulb mode and on the AH501BE in External Gate mode AveragingTime should be set to 0. The driver will force the averaging to occur each time it detects the falling edge of the gate pulse. This means that it will use the readings that happened while the gate pulse was high.

QE_NUM_AVERAGE

$(P)$(R)NumAverage_RBV

longin

asynInt32

r/o

All

Provides the number of values that will be accumulated in the ring buffer before they are read out into NDArray objects and any registered plugins are called. NumAverage_RBV is computed as (int)((AveragingTime / SampleTime_RBV) + 0.5). , On the TetrAMM when TriggerMode=External Bulb and on the AH501BE when TriggerMode=External Gate the AveragingTime is ignored and NumAverage_RBV will be 0. The averaging is done on all samples collected when the external gate signal is asserted.

QE_NUM_AVERAGED

$(P)$(R)NumAveraged_RBV

longin

asynInt32

r/o

All

Provides the number of values that were actually accumulated in the ring buffer before they were read out into NDArray objects and any registered plugins were called. If AveragingTime>0 then NumAveraged_RBV will be the same as NumAverage_RBV. However, if AveragingTime=0. then NumAverage_RBV=0 and NumAveraged_RBV gives the actual number of values read from the ring buffer when the ReadData record was processed. This is also true on the TetrAMM when TriggerMode=ExternalBulb.

N.A.

$(P)$(R)FastAveragingTime, $(P)$(R)FastAveragingTime_RBV

ao, ai

asynFloat64

r/w

All

Controls the time period over which values are averaged with the “fast averaging” support when FastAverageScan.SCAN=I/O Intr. This value is converted to NumFastAverage, which is then written to the .SVAL field of each ai record.

N.A.

$(P)$(R)NumFastAverage

longin

asynInt32

r/o

All

Provides the number of values that will be averaged in the “fast averaging” support. NumFastAverage is computed as (int)((FastAveragingTime / SampleTime_RBV) + 0.5).

QE_NUM_ACQUIRE

$(P)$(R)NumAcquire , $(P)$(R)NumAcquire_RBV

longout , longin

asynInt32

r/w

All

The number of acquisitions to acquire when AcquireMode=Multiple. An acquisition is complete when the callbacks are called. This normally occurs when the AveragingTime has elapsed. However when TriggerMode=Ext. Bulb then the callbacks are called and an acquisition is complete on the trailing edge of each external gate pulse.

QE_NUM_ACQUIRED

$(P)$(R)NumAcquired

longin

asynInt32

r/o

All

The number of acquisitions completed since Acquire was set to 1.

QE_READ_DATA

$(P)$(R)ReadData

busy

asynInt32

r/o

All

Writing 1 to this record reads all data from the ring buffer and does the NDArray callbacks to all registered plugins. This is typically done when the quadEM is being used for data acquisition, for example in a scan. In this case AveragingTime is set to 0 and processing the ReadData record will read all values that have accumulated in the ring buffer since ReadData was last processed.

QE_RING_OVERFLOWS

$(P)$(R)RingOverflows

longin

asynInt32

r/o

All

It is possible for the ring buffer to overflow. The rate at which values are added to the ring buffer is controlled by SampleTime_RBV. The rate at which values are removed is determined by AveragingTime, or by the rate at which ReadData is processed if AveragingTime=0. The size of the ring buffer is determined by the ringBufferSize argument to the driver constructor. This defaults to 2048 if it is not specified in configuration command in the startup script. If the ring buffer is full when the driver tries to add a new value, then the oldest value in the buffer is discarded, the new value is added, and RingOverflows is incremented. RingOverflows is set to 0 the next time the ring buffer is read out.

QE_TRIGGER_MODE

$(P)$(R)TriggerMode

mbbo

asynInt32

r/w

TetrAMM, AH501, AH401, and PCR4

Allowed choices are:

  • 0: “Free Run” (all models). Ignores any external gate or trigger signal.

  • 1: “Software” (possible future choice for TetrAMM) This will trigger a single acquisition each time a software trigger command is sent.

  • 2: “Ext. Trigger” (AH401B, TetrAMM, PCR4) This is an edge-sensitive trigger. On the TetrAMM this will collect samples for the AveragingTime and then wait for the next trigger.

  • 3: “Ext. Bulb” (AH501D, TetrAMM) This is a level-sensitive trigger. It acquires data while the external gate signal is asserted. On the trailing edge of the gate signal the callbacks will be called. In this mode the AveragingTime is ignored and the averaging is done for all samples received between the leading and trailing edge of a single gate pulse.

  • 4: “Ext. Gate” (TetrAMM) This is a level sensitive gate. It acquires data while the external gate signal is asserted. However, unlike Ext. Bulb the trailing edge of the gate signal is ignored, and the averaging is done for NumAverage_RBV samples as with Free Run mode. The difference is that the actual averaging time will be longer than AveragingTime, and is controlled by the duty cycle of the external gate pulse. If the external gate pulse is asserted 40% of the time, then the actual averaging time will be AveragingTime * 2.5

QE_TRIGGER_POLARITY

$(P)$(R)TriggerPolarity

mbbo

asynInt32

r/w

PCR4

0=Positive, 1=Negative.

QE_RESET

$(P)$(R)Reset

bo

asynInt32

r/w

All

Reset command. Processing this record will reset the electrometer. On the TetrAMM this does a hardware reset of the device, which takes about 10 seconds. On all models this operation downloads all of the EPICS settings to the electrometer. The Reset reord must be processed if any electrometer is power-cycled without rebooting the EPICS IOC.

QE_CURRENT_NAME

$(P)$(R)CurrentName[1-4]

stringin

N.A.

r/w

All

User-defined name to give each of the Current[1-4] inputs.

N.A.

$(P)$(R)Current[1-4]Ave

ai

asynFloat64 (addr=0-3)

r/o

All

Average current computed by the fast averaging support.

N.A.

$(P)$(R)Sum[X,Y,All]Ave

ai

asynFloat64 (addr=4-6)

r/o

All

Average sum (X, Y, All) computed by the fast averaging support.

N.A.

$(P)$(R)Diff[X,Y]Ave

ai

asynFloat64 (addr=7-8)

r/o

All

Average difference (X, Y) computed by the fast averaging support.

N.A.

$(P)$(R)Position[X,Y]Ave

ai

asynFloat64 (addr=9-10)

r/o

All

Average position (X, Y) computed by the fast averaging support.

QE_CURRENT_OFFSET

$(P)$(R)CurrentOffset[1-4]

ao

asynFloat64 (addr=0-3)

r/w

All

Offset that will be subtracted from each reading when calculating the Current[1-4]. The current is calculated as Current = Raw*CurrentScale - CurrentOffset, where Raw is the raw value from the device.

N.A.

$(P)$(R)ComputeCurrentOffset[1-4]

calcout

N.A.

r/w

All

Processing this record will compute a new value of CurrentOffset that will set value of the current to 0 under the current conditions. It computes CurrentOffset(new) = Current[1-3]:MeanValue_RBV + CurrentOffset(old). This record is provided to convenience set the CurrentOffset when the input signal is 0.

QE_CURRENT_SCALE

$(P)$(R)CurrentScale[1-4]

ao

asynFloat64 (addr=0-3)

r/w

All

Scale factor that each reading is multiplied by when calculating the Current[1-4]. The current is calculated as Current = Raw*CurrentScale - CurrentOffset, where Raw is the raw value from the device. This record provides a way to convert the current readings into engineering units. All of the models except the TetrAMM transmit integer data. This is converted to double precision float for averaging and statistics. It is converted back to integer for the time series software, which requires integer data. The TetrAMM transmits double precision data in units of amps, so the values are typically between 1e-4 to 1e-12. It is convenient to use a CurrentScale of 1e9 or 1e12, for example, so that the data are displayed in units of nano-amps or pico-amps. They are then reasonable sized integers, and the time series software can be used.

N.A.

$(P)$(R)CurrentPrec[1-4]

mbbo

N.A.

r/w

All

Precision (# digits) to use to display the current for this channel. Choices are 0-9. CurrentPrec1 also controls SumX and DiffX. CurrentPrec3 also controls SumY and DiffY. CurrentPrec2 also controls SumAll. Note that when using medm and other display clients it is necessary to close and re-open the quadEM screen for the displayed precision to be changed. This is a limitation of the Channel Access protocol which does not send monitor events when the precision is changed.

QE_POSITION_OFFSET

$(P)$(R)PositionOffset[X,Y]

ao

asynFloat64 (addr=0-1)

r/w

All

Offset that will be subtracted from each reading when calculating the Position[X,Y]. The position is calculated as Position = Diff/Sum * PositionScale - PositionOffset.

N.A.

$(P)$(R)ComputePosOffset[X,Y]

calcout

N.A.

r/w

All

Processing this record will compute a new value of PositionOffset that will set value of the position to 0 under the current conditions. It computes PositionOffset(new) = Pos[X,Y]:MeanValue_RBV + PositionOffset(old). This record is provided to convenience set the PositionOffset when the position should be defined as 0.

QE_POSITION_SCALE

$(P)$(R)PositionScale[X,Y]

ao

asynFloat64 (addr=0-1)

r/w

All

Scale that will be used when calculating the Position[X,Y]. The position is calculated as Position = Diff/Sum * PositionScale - PositionOffset.

N.A.

$(P)$(R)PositionPrec[X,Y]

mbbo

N.A.

r/w

All

Precision (# digits) to use to display the position in X or Y. Choices are 0-9.

QE_CALIBRATION_MODE

$(P)$(R)CalibrationMode

bo

asynInt32

r/w

NSLS2_EM

Puts driver in calibration mode where ADC offsets can be computed. Choices are Off (0) and On (1). The Calibration mode is used to compute the ADC offsets.

N.A.

$(P)$(R)ADCOffset[1-4]

longout

N.A.

r/w

NSLS2_EM

ADC offset for this channel.

N.A.

$(P)$(R)CopyADCOffsets

transform

N.A.

r/w

NSLS2_EM

Processing this record will copy the current reading from each channel into the ADCOffset[1-4] records. This should only be done when CalibrationMode=On. This does an ADC offset calibration that is independent of the Range of the device.

The following is the medm screen to control the quadEM with the records in quadEM.template.

_images/quadEM.png