1. Calibration of the PotAim cards and chassis

Document information

Tags/Project: Test-Procedures-wiki

Metadata Field	Document Information
Status	Draft
Created	2026-09-24
Last Updated	2026-10-01
Author	Davide Cuneo
Rev. #	0.4
Reviewers	TBD

Source documents. This procedure is based on the CERN reference procedure “Procedure PotAim with crate – Calibration” (Rev. 0, G. Dib, 14 July 2011) and on the notes taken by Davide Cuneo during the practical demonstration given by Jean Luc Guyon at CERN.

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Introduction and Context

This procedure describes the operative steps necessary to calibrate the POTAIM cards (PotAim cards, PAC) together with their associated crate at FREIA Laboratory. It must be used as the reference procedure for this operation. Jean Luc Guyon at CERN in SM18 performs it at the beginning of every year. The procedure recall what is being done at CERN with their equipment and is adapted for the operations in FREIA.

According to the parameters used during dipole or quadrupole tests on the horizontal benches in SM18, the nominal procedure consists in checking and adjusting the different functionalities of a POTAIM card:

1. Power supply adjustment (crate ±15 V);
2. Check of the general aspect of the card;
3. Offset and gain adjustment;
4. Trigger function check (threshold, trigger channel checking, delay).

Order of operations

The calibration sequence described in this procedure must be performed in the order given below. The success of the gain calibration depends on the adjustment of the ±15 V power supply and on the offset.

At CERN the operation is carried out with a dedicated adapter card into which the PotAim card is inserted (Figure 1). AT FREIA Laboratory the adapter card presents a slightly different aspect.

Few words about the PotAim cards

Each PotAim card is composed of two channels (canals), A and B. Each channel amplifies the voltage applied between its positive and negative inputs by the selected gain. The output of a channel is:

$V_{out}=G\cdot ((V_{+}-V_{-})+V_{offset})$

When the inputs are short-circuited, which reproduces what is expected from a superconducting magnet (zero voltage), the output should read zero. In practice a residual offset is measured and must be zeroed.

The available gains in the card are ×1.2, ×4, ×10 and ×40, plus a :100 divider used in combination with gain 40 (effective gain 0.4). The selected gain is shown by a green LED on the front of the card (Figure 12).

Front-panel elements used in this procedure:

Element	Function
Green LEDs (X1.2, X4, X10, X40, :100)	Display of the selected gain
OFFSET potentiometer (one per channel)	Offset adjustment
OUT A / OUT B (LEMO)	Channel output, read with the multimeter
SEUIL DECL. (LEMO)	Threshold displayed, read with the multimeter
LD1 (red LED)	Indicates that a trigger happened
SW1	Trigger function selection switch (TCA / TCB)
BP1	Push-button used to trigger the card
SYNCH. (LEMO)	Synchronisation outputs used for the delay check
P1	Delay potentiometer

The threshold displayed on the card already accounts for the gain: threshold displayed = threshold × gain. For example, a threshold of 100 mV with gain 40 gives 4000 mV displayed.

Required Material

Tooling

1. Adapter card (Figure 1);
2. Screwdrivers (a small one is needed to reach the potentiometers through the front-panel holes);
3. “Grip-fils” hook clips (Figure 2);
4. LEMO cables, LEMO-to-BNC adapters and banana connectors for shorting the input wires.

Instrumentation

1. Oscilloscope mounted on the Data Acquisition rackj;
2. DC calibrator voltage source, Rohde & Schwarz HMP2020
3. High-precision voltmeter/multimeter (Fluke 8842A or Keithley 2001).

Documents

1. Excel file in which the data are filled in
2. Calibration Procedure from CERN

Test preparation

Visual check

Perform a visual check of the general state of the card, looking for broken components or welds, burned components, etc.

Record the original parameters

According to the standard tests in the SM18 horizontal benches, each PotAim card is configured with its own gain, threshold and delay. Before changing anything, note down the original parameters of the cards under calibration (gain, threshold, delay and position of the input jumpers), so that they can be restored at the end. These parameters should note in the Excel file.

About the Excel file

This file does not have a proper standard template so it might be necessary to set one

Power supply crate adjustment

The power supply of the PotAim cards inside the crate is a VERO PK60 BIVOLT. Its stabilised output must be checked and set to ±15 V.

Warning

The crate must NOT be powered during the first three steps below.

1. Check that the crate is equipped with 10 PotAim cards.
2. Insert the adapter card in the first slot, between the crate and a PotAim card (Figure 4).
3. On the J2 connector of the PotAim card, connect three grip-fils on the terminals C28, C30 and C32 (Figures 5 and 6).

4. Power the multimeter and the crate, then wait 15–20 min.

Warning

From this point on, and as long as the crate is powered, it is forbidden to remove the grip-fils. A short circuit could occur and damage the power supply.

The two potentiometers used to adjust the ±15 V are located on the power supply, at the back of the crate (Figure 7).

5. Connect C30 to the High input and C32 to the Low input of the multimeter, and measure the +15 V. Adjust it within ±0.1 V with potentiometer V1.
6. Connect C28 to the High input and C32 to the Low input of the multimeter, and measure the −15 V. Adjust it within ±0.1 V with potentiometer V2.
7. The power supply must be stable and the voltages as close as possible to ±15 V. If this is not the case, replace the power supply with a new one and put a sticker on it with the removal date.
8. Fill in the Excel file.
9. Switch off the crate, then remove the three grip-fils from the PotAim card. Only then switch the crate back on.

Measurement	Multimeter High	Multimeter Low	Potentiometer	Nominal	Tolerance
+15 V	C30	C32	V1	+15 V	±0.1 V
−15 V	C28	C32	V2	−15 V	±0.1 V

Offset adjustment

The following sequence must be performed for each card, on both channels A and B.

1. Place the input jumpers in position ST3 for channel A and ST1 for channel B (Figure 8). The jumpers configure the card for direct or differential input voltage. Note down their original state.

2. Short together the four input wires of the adapter card, labelled ChA+, ChA−, ChB+ and ChB− (Figure 9).

3. Connect a LEMO cable from the OUT A output on the front of the card to the High and Low inputs of the multimeter, and measure the offset. Adjust it to ±1 mV with the OFFSET potentiometer on the front, inserting the screwdriver in the hole (Figure 12).

Warning

Be careful to use the correct OFFSET potentiometer: there is one dedicated to each channel.

4. Fill in the Excel file with the new offset (Excel file link to be added).
5. Repeat steps 3 and 4 for OUT B.

Offset for each gain?

The offset differs from gain to gain. It is still to be clarified whether the offset has to be zeroed for every gain or only for gain 40, which has the highest offset. During the demonstration given at CERN Jean Luc started from gain 1.2 (without the :100 divider) and showed that the output was close to 0 V.

Gain adjustment

The wiring for the gain adjustment is shown in Figure 13.

1. Connect ChA+ and ChB+ to the High terminal of the DC calibrator.
2. Connect ChA− and ChB− to the Low terminal of the DC calibrator.
3. Switch on the DC calibrator.
4. Check that the LEMO from the card output is still connected to the multimeter (Figure 14).

5. Check that the gain displayed by the green LED on the front of the card corresponds to the gain in the Excel file table.
6. Apply the voltages with the DC calibrator following Table 1. For each gain, activate the corresponding switch (column ON) and adjust with the corresponding potentiometer (column Adjustment).

Table 1: Gain calibration settings. Input voltage applied on pins Z4–Z12 for channel A and D22–D30 for channel B.

Gain	V in	Ch. A – ON	Ch. A – Adjustment	Out A	Ch. B – ON	Ch. B – Adjustment	Out B
40	+0.2 V	SW8	P14	+8 V	SW4	P6	+8 V
40	−0.2 V	SW8	P14	−8 V	SW4	P6	−8 V
10	+1.0 V	SW9	P15	+10 V	SW5	P7	+10 V
10	−1.0 V	SW9	P15	−10 V	SW5	P7	−10 V
4	+2 V	SW10	P16	+8 V	SW6	P8	+8 V
4	−2 V	SW10	P16	−8 V	SW6	P8	−8 V
1.2	+8 V	SW11	P17	+9.6 V	SW7	P9	+9.6 V
1.2	−8 V	SW11	P17	−9.6 V	SW7	P9	−9.6 V
40 /100	+10 V	SW8/SW3	P10	+4 V	SW4/SW2	P4	+4 V
40 /100	−10 V	SW8/SW3	P10	−4 V	SW4/SW2	P4	−4 V

7. Adjust the gain by measuring the output voltage against the voltage applied on the inputs, and fill in the Excel file. The adjustment must take both the positive and the negative reading into account.

Example: Crate 2 for dipole, Card 1, Channel A

The configuration of the channel is given in Table 2. According to Tables 1 and 2, gain 40 is adjusted with potentiometer P14 using ±0.2 V from the DC calibrator. First apply +0.2 V and read the output, then apply −0.2 V and read the new output. The adjustment must consider both values, at +0.2 V and −0.2 V.

Table 2: Configuration of Crate 2 (dipole), Card 1, Channel A.

Channel definition	Gain	Threshold	Validation time (ms)
V_Lead_C	40	100	5

8. Repeat steps 5 to 7 for OUT B (channel B).
9. Switch off the DC calibrator.

Warning

Once the gain adjustment is finished, the input jumpers (ST3 for channel A and ST1 for channel B) must be put back in their initial position.

Threshold adjustment

The threshold is used to protect the magnet during the tests on the horizontal bench.

1. Connect the LEMO output labelled SEUIL DECL. on the front of the card to the multimeter.
2. Adjust the threshold displayed with the potentiometer, according to the value required in the Excel file (Figure 16).

Trigger channel checking

The red LED LD1 on the front of the PotAim card shows that a trigger happened. Check that both channels send the trigger information to this LED (Figure 17).

1. Short together the four input wires of the adapter card, ChA+, ChA−, ChB+ and ChB− (Figure 9).
2. With the trigger function selection switch SW1, activate channel TCA, then trigger the card by pressing BP1. BP1 must be kept pressed for at least the validation time.
3. The trigger LED LD1 should switch on.
4. Repeat steps 2 and 3 for TCB.

Warning

TCA and TCB must never be ON at the same time!

Trigger card delay

The LED LD1 must not be ON at the start of this check. To switch LD1 off, short together the four wires ChA+, ChA−, ChB+ and ChB−.

1. Connect the two LEMO outputs on the front of the PotAim card (Figure 17) to an oscilloscope.
2. Configure the oscilloscope to trigger on the negative slope of the Synchro output, and check that the time duration of the other signal corresponds to the delay required in the Excel file (Figure 18).
3. Adjust the delay with potentiometer P1.

After the test

Once all the checks have been completed on every card:

1. Verify that the input jumpers of each card are back in their initial position (ST3 for channel A, ST1 for channel B, as noted at the beginning).
2. Verify that gain, threshold and delay of each card match the original parameters recorded in the Excel file.
3. Complete the Excel file with all measured values.
4. Put a checking sticker on each calibrated card with the date and the operator’s name.
5. Remove the adapter card and put the PotAim cards back in their original slots (step not explicitly described in the CERN procedure, to be confirmed).

Operational Checklist

To be filled in during execution, in order.

Preparation

• Performed the visual check of each card (broken components or welds, burned components)
• Recorded the original gain, threshold, delay and input jumper positions of each card in the Excel file

Power supply crate adjustment

• Crate NOT powered
• Checked that the crate is equipped with 10 PotAim cards
• Inserted the adapter card in the first slot, between the crate and a PotAim card
• Connected three grip-fils on terminals C28, C30 and C32 of J2
• Powered the multimeter and the crate and waited 15–20 min (grip-fils NOT removed while powered)
• Measured and adjusted +15 V (C30 High, C32 Low) within ±0.1 V with V1
• Measured and adjusted −15 V (C28 High, C32 Low) within ±0.1 V with V2
• Power supply stable and close to ±15 V (otherwise replaced and sticker with removal date applied)
• Filled in the Excel file
• Switched off the crate, removed the three grip-fils, switched the crate back on

Offset adjustment (for each card)

• Input jumpers set to ST3 (channel A) and ST1 (channel B), original state noted
• Shorted ChA+, ChA−, ChB+ and ChB− together
• OUT A connected to the multimeter via LEMO; offset adjusted to ±1 mV with the channel A OFFSET potentiometer
• Filled in the Excel file with the new offset of channel A
• Repeated for OUT B and filled in the Excel file

Gain adjustment (for each card)

• Connected ChA+ and ChB+ to the DC calibrator High, ChA− and ChB− to the DC calibrator Low
• Switched on the DC calibrator and checked that the output LEMO is connected to the multimeter
• Checked that the gain LED matches the gain in the Excel file
• Gain 40 (±0.2 V → ±8 V) adjusted and recorded, channel A and B
• Gain 10 (±1.0 V → ±10 V) adjusted and recorded, channel A and B
• Gain 4 (±2 V → ±8 V) adjusted and recorded, channel A and B
• Gain 1.2 (±8 V → ±9.6 V) adjusted and recorded, channel A and B
• Gain 40 /100 (±10 V → ±4 V) adjusted and recorded, channel A and B
• Switched off the DC calibrator
• Input jumpers ST3 (A) and ST1 (B) put back in their initial position

Threshold adjustment (for each card)

• SEUIL DECL. connected to the multimeter; threshold displayed adjusted to the Excel value, channel A and B

Trigger channel checking (for each card)

• Shorted ChA+, ChA−, ChB+ and ChB− together
• SW1 on TCA, BP1 pressed for the validation time, LD1 switched on
• SW1 on TCB, BP1 pressed for the validation time, LD1 switched on
• Verified that TCA and TCB were never ON at the same time

Trigger card delay (for each card)

• LD1 switched off (four input wires shorted)
• Two front LEMO outputs connected to the oscilloscope, trigger on negative slope of Synchro
• Delay checked against the Excel file and adjusted with P1 if needed

After the test

• Input jumpers, gain, threshold and delay back to the original values
• Excel file completed
• Checking sticker (date and operator) applied on each card
• Adapter card removed and cards back in their original slots

Feedback

Found an error or something outdated in this note? Please contact Davide Cuneo (davide.cuneo@physics.uu.se).