Summary:
The hardware injection inverse actuation filter has the correct amplitude and sign. This is tested using a known sinusoidal waveform and comparing the Pcal RXPD readback with the input to the inverse actuation filter. See attached figure.

Details:
Similar to my investigation of the sign of the inverse actuation filter (LHO aLOG 29072), I injected a 100 Hz signal, 1e-23 in strain amplitude, 0 phase using awgstream into H1:CAL-PINJX_TRANSIENT_EXC.

To verify the injection has the right amplitude and sign, I read out H1:CAL-PINJX_TRANSIENT_IN2 and H1:CAL-PCALX_RX_PD_OUT_DQ. The time-series data for both channels is bandpassed with a filter centered around 100 Hz. In this measurement, I did not turn on the [:1,1] filter (FM7) for the PCAL readback channel. Instead, I scaled the readback signal by -1e-4 (=-100^2). Also, I had to make an offset since there is a DC component to the Pcal signal. The TRANSIENT_IN2 has its time-series scaled by 4000 to convert between strain and meters.

The attached figure shows that the amplitude is nearly spot on, the sign is correct, and the known phase offset (~240 usec) is understood from the inverse actuation filter for the TRANSIENT injection path.

Thus, the inverse actuation filter for hardware injections is correct in amplitude and sign.